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In this work we address the stability of riebeckite at high temperatures and compare the different behaviors observed under various oxidation conditions. For this purpose, we annealed powders of a sample from Mt. Malosa (Malawi), which is compositionally close to the end-member; the run products obtained after annealing in air vs. in vacuum were studied by Mössbauer spectroscopy and powder X-ray diffraction. The results show that riebeckite follows two distinct paths depending on the external environment. Under oxidizing conditions, it is stable in the hydrous form up to relatively low temperatures (400–450 °C), then it undergoes a rapid (within ~50 °C) dehydrogenation, forming oxo-riebeckite, which is stable up to ~900 °C. The final breakdown products of the oxo-amphibole include aegirine + cristobalite + hematite. Based on the relative intensity of the (310) Bragg reflection, the activation energy (Ea) for the riebeckite to oxo-riebeckite transition is 166 ± 6 kJ/mol. Under vacuum conditions, no Fe oxidation is observed, and riebeckite is stable up to much higher temperatures (750–800 °C); however, in the 550 < T < 700 °C range, it undergoes a significant re-arrangement of the C cations (those hosted in the strip of octahedra). Indeed, the amphibole stable in the 700–800 °C range has the same chemical formula as riebeckite but has a disordered and nonstandard cation distribution at the octahedra, i.e., M(1)(Fe3+Fe2+)M(2)(Fe3+Fe2+)M(3)Fe2+; we call this phase “CR3+ disordered riebeckite”. For T ≥ 800 °C, it decomposes to aegirine + fayalite + cristobalite + H2O. External oxygen is required for the release of water into the surrounding system, being a prerequisite for the Fe-amphiboles to be a carrier of H2O in the lower crust and upper mantle. One important implication of our results is that characterization of the overall oxidation state of iron does not necessarily provide the redox conditions of the environment of formation because a crystal-chemical re-arrangement under reducing conditions allows riebeckite to maintain its Fe3+/Fe2+ composition up to higher temperatures.

Ferro-papikeite, ideally NaFe22+(Fe32+Al2)(Si5Al3)O22(OH)2, is a new mineral of the amphibole supergroup from the Filipstad Municipality, Värmland County, Central Sweden, where it occurs in a medium-grade felsic metavolcanic rock. Ferro-papikeite is pale brown with a translucent luster, has a colorless to very pale-brown streak, and shows no fluorescence under long-wave or short-wave ultraviolet light. Grains are subhedral, 0.4–3.0 mm in size, and show well-developed {210} cleavage. It has a Mohs hardness of ~6 and is brittle with a splintery fracture, has the characteristic perfect {210} cleavage of orthorhombic amphiboles, intersecting at ~56°, and the calculated density is 3.488 g/cm3. In transmitted plane-polarized light, ferro-papikeite is moderately pleochroic X = very pale brown, Y = Z = honey brown; X < Y = Z. Ferro-papikeite is biaxial (+), α = 1.674(2), β = 1.692(2), γ = 1.716(2), 2Vmeas = 86.2(9) and 2Vcalc = 88.3°, dispersion is r < v, weak. The orientation is: X || a, Y || b, Z || c. Ferro-papikeite is orthorhombic, space group Pnma, a = 18.628(4), b = 17.888(4), c = 5.3035(11) Å, V = 1767.2(6) Å3, Z = 4. The strongest ten X-ray diffraction lines in the powder pattern are [d in Å(I) (hkl)]: 8.255(100)(210), 3.223(39)(440), 3.057(68)(610), 2.824(28)(251), 2.674(41)(351), 2.572(56) (161,621), 2.549(38)(202), 2.501(50)(261,451), 2.158(25)(502), and 1.991(31)(661). Chemical analysis by electron microprobe gave SiO2 36.50, Al2O3 22.24, TiO2 0.09, FeO 31.54, MnO 0.65, MgO 5.48, CaO 0.08, Na2O 2.35, F 0.22, H2Ocalc 1.85, O=F –0.09, sum 100.91 wt%. The formula unit, calculated on the basis of 24 (O+OH+F) with (OH) = 2 apfu and Fe3+ = 0.13 apfu (determined from the distance) is A(Na0.70Ca0.01)B+C(Mg1.25Fe3.902+Mn0.082+Al1.62Fe0.132+Ti0.014+)Σ6.99T(Si5.60Al2.40)Σ8O22(OH1.89F0.11)2. The crystal structure of ferro-papikeite was refined to an R-index of 3.60% using 2335 unique observed reflections collected with MoKa X-radiation. [4]Al3+ is ordered over the four T sites as follows: T1B > T1A > T2B >> T2a, [6]Al3+ is completely ordered at M2, and Fe2+ is strongly ordered at M4. The A site is split with Na+ strongly ordered at A1. End-member ferro-papikeite is related to end-member gedrite, ☐Mg2(Mg3Al2)(Si6Al2)O22(OH)2, by the substitutions Na+ → ☐, Fe2+ → Mg, and Al3+ → Si4+. The description of ferro-papikeite as a new species further emphasizes the compositional similarities between the monoclinic calcium amphiboles and the orthorhombic magnesium-iron-manganese amphiboles.

The ideal formulae of two root-names of the hellandite group, i.e. mottanaite and ciprianiite, were originally given as Ca-X(4)Y(CeCa)(2)(AlBe2)-Al-Z-Be-T[B4Si4O22]O-W(2) and Ca-X(4)Y(Th,U)REE](Sigma 2)Al-Z(T) square(2)[B4Si4O22](W)(OH)(2). In order to conform to the later introduced dominant-valency nomenclature rule, they have been redefined as (Ca4REE2AlT)-Ca-X-R-Y-Al-Z(Be-1.5 square(0.5))[B4Si4O22]O-W(2) and Ca-X(4)Y [Th,U)Ca](Sigma 2)Al-Z(T) (Be-0.5 square(0.5))(Sigma 2)[B4Si4O22](W)(OH)(2), respectively (IMA-CNMNC vote 18D). Also, the mineral description is provided for the first Fe3+ -dominant species of the hellandite group, ferri-mottanaite-(Ce), ideally Ca-X(4)Y (Ce2Fe3+T)-Fe-Z (Be-1.5 square(0.5)) [Si4B4O22]O-W(2). The type specimen was found in an ejectum collected at Tre Croci (Vetralla, Vico volcanic province, Italy). The empirical formula derived from electron microprobe and LA-ICP-MS analyses, and validated by single-crystal structure refinement is: X(Ca)(4)(Y)(Ca0.40REE0.93 (Th,U)(0.54)(4+)square(0.13))(Sigma 2.00) (Z)(Fe0.503+Al0.23Mn0.173+Ti0.174+)(Sigma 1.07)(T)(B1.04Li0.04 square(0.92))=Sigma(2.00)[Si4.03B3.89O22] (O-1.09(OH)(0.38)F-0.53)(Sigma 2.00.) Ferri-mottanaite-(Ce) is biaxial (-), with alpha = 1.748(5), beta = 1.762(5), gamma = 1.773(5) and 2V (meas.) = 85.9(5)degrees, 2V (calc.) = 82.5 degrees. The unit-cell parameters are a = 19.0548(9), b = 4.7468(2), c = 10.2560(5) angstrom, beta = 110.906(2)degrees, V = 866.58(7) angstrom(3) , Z = 2, space group P2/a. The strongest reflections in the X-ray powder pattern obtained from single-crystal data [d values (in angstrom), I, (hkl)] are: 2.648, 100, (013,(4) over bar 13); 2.857, 50, (411); 1.904, 48, (023,(4) over bar 23,621); 2.919, 44, (212); 3.086, 44, ((4) over bar 12); 3.246, 43, ((4) over bar 10); 3.453, 36, ((2) over bar 12); 4.745, 33, (010).

We present the results of a comprehensive study linking the crystal-chemical formulae of amphiboles, a series of extremely complex silicates with the general formula (ABCTOW, C = M1M2M3) to variations in the peak positions, widths, and intensities of the Raman-active modes. To this purpose, we have analyzed the Raman scattering generated by the framework vibrations (15-1,215 cm) and by the OH-stretching modes (3,000-4,000 cm) of 44 samples, spanning all six major subgroups. We show that, in addition to the information that can be derived from the OH-stretching range (Leissner et al., Am. Mineral. 2015, 100, 2682), further important features of the amphibole structure, composition, and cationic site population can be directly extracted from the framework Raman spectrum, namely, (a) the distinction between the monoclinic and orthorhombic symmetries; (b) the estimation of Al content, when Al > 0.5 apfu; (c) the estimation of Ti content, when Ti > 0.3 apfu; (d) the estimation of Li content, when Li > 0.3 apfu; (e) the detection of Al, when Al > 0.7 apfu; (f) an estimate of Mg; (g) the estimation of Fe in the case of Na amphiboles; and (h) the estimation of the Fe content at the M2 site in the case of Mg-Fe-Mn amphiboles. Additionally, we point out that the TO-ring-breathing mode near 670 cm, which is commonly used to fingerprint various amphibole species, has to be handled with a great care, because it is sensitive to the site population at all crystallographic sites.

Magnesio-hornblende (IMA2017-059) has been characterized in a specimen collected in the sand dunes of Lüderitz, Karas Region, Namibia. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is A(□0.73Na0.22K0.05)Σ1.00B(Ca1.79Fe2+0.10Mg0.04Mn2+0.03Na0.04)Σ2.00C(Mg3.48Fe2+0.97Al0.28Fe3+0.23Cr3+0.01Ti0.03)Σ5.00T(Si7.18Al0.82)Σ8.00O22W[(OH)1.93F0.05Cl0.02]Σ2.00. Magnesio-hornblende is biaxial (–), with α = 1.640(2), β = 1.654(2), γ = 1.666(2) (measured with gel-filtered Na light, λ = 589.9 nm), 2V (meas.) = 82(1)° and 2V (calc.) = 84.9°. The unit-cell parameters are a = 9.8308(7), b = 18.0659(11), c = 5.2968(4) Å, β = 104.771(6)° and V = 909.64 (11) Å3 with Z = 2 and space group C2/m. The strongest eight reflections in the X-ray powder pattern [d values (in Å), I, (hkl)] are: 2.709, 100, (151); 8.412, 74, (110); 3.121, 73, (310); 2.541, 58, ($\bar{2}$02); 3.386, 49, (131); 2.596, 45, (061); 2.338, 41, ($\bar{3}$51); and 2.164, 39, (261).

In this work we report on a complete crystal-chemical characterization of a near end-member riebeckite from Malawi, and use the available data to critically compare information obtained from different analytical methods. The sample occurs as well-formed and very large single crystals in pegmatitic rocks. Accurate site-populations were determined by combining single-crystal structure refinement and electron microprobe analysis (EMPA). The Fe3+/Fe2+ ratio was obtained from Mössbauer spectroscopy. Lithium was quantified by Laser Ablation Inductively Coupled Plasma Mass Spectroscopy (LA-ICP-MS).Fourier-Transform Infrared (FTIR) spectra, collected both on powders and single crystals, are presented and discussed. FTIR spectra in the NIR region are also presented for the first time for this amphibole. The FTIR data are compatible with complete local ordering of A cations close to F, and complete Fe2+/Mg disorder at M(1,3). Polarized Raman-scattering data collected from single crystals confirm this conclusion. In addition, it was found that FTIR data collected on powders provide the best agreement with the site occupancies derived from chemical (EMPA and LA-ICP-MS) and crystal-chemical data, possibly because they do not depend on experimental issues such as orientation and polarization.

The mineral description is provided for ferro-tschermakite, ideally (A)square Ca-B(2)C(Fe32+Al2)(T)(Si6Al2)O-22(W)(OH)(2). The type specimen has been found in the dump of the Batiment et Granit de Ploumanac'h northern granite quarry, La Clarte, Perros-Guirec, Ploumanac'h granitic complex, Brittany, France. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: (A)(Na0.29K0.08)(Sigma= 0.37)(B)(Ca1. 69Fe0. 112+Mn0.022+Na0.18)(Sigma=2.00)(C)(Fe1. 842+Mg1.54Al1.33Fe0.243+V0.013+ Ti-0.04)(Sigma= 5.00)(T)(Si6.15Al1.85)(Sigma= 8.00)O-22(W)(OH1.94F0.06)(Sigma= 2.00). Ferro-tschermakite is biaxial (-), with alpha = 1.666(2), beta = 1.680(2), gamma = 1.690(2) and 2V (meas.) = 84(1)degrees, 2V (calc.) = 79.8. The dispersion is medium (r> v), and the orientation is: X a = 9.5 degrees (in beta acute), Y || b, Z c = 24.3 degrees (in beta obtuse). The unit-cell parameters are a = 9.7598(6), b = 18.0220(11), c = 5.3299(3) angstrom, beta = 104.826(1)degrees, V = 906.27 (9) angstrom, Z = 2, space group C2/m. The strongest ten reflections in the X-ray powder pattern obtained from single-crystal data [d values (in angstrom), I, (h k l)] are: 8.359, 100, (1 1 0); 2.708, 84, (1 5 1); 3.098, 55, (3 1 0); 2.552, 43, ((2) over bar 0 2); 2.595, 41, (0 6 1); 2.330, 33, ((3) over bar 5 1); 2.159, 27, (2 6 1); 2.936, 27, (2 2 1); 3.338, 27, (1 3 1); 2.012, 24, ((4) over bar 0 2; 3 5 1).

Clino-suenoite, ideally □${\rm Mn}_{2}^{2 +} $Mg5Si8O22(OH)2 is a new amphibole of the magnesium-iron-manganese subgroup of the amphibole supergroup. The type specimen was found at the Lower Scerscen Glacier, Valmalenco, Sondrio, Italy, where it occurs in Mn-rich quartzite erratics containing braunite, rhodonite, spessartine, carbonates and various accessory minerals. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: ANa0.04B(${\rm Mn}_{1.58}^{2 +} $Ca0.26Na0.16)Σ2.00C(Mg4.21${\rm Mn}_{0. 61}^{2 +} {\rm Fe}_{0.04}^{2 +} $Zn0.01Ni0.01${\rm Fe}_{0.08}^{3 +} $Al0.04)Σ5.00TSi8.00O22W[(OH1.94F0.06)]Σ=2.00. Clino-suenoite is biaxial (+), with α = 1.632(2), β = 1.644(2), γ = 1.664(2) and 2Vmeas. = 78(2)° and 2Vcalc. = 76.3°. The unit-cell parameters in the C2/m space group are a = 9.6128(11), b = 18.073(2), c = 5.3073(6) Å, β = 102.825(2)° and V = 899.1(2) Å3 with Z = 2. The strongest ten reflections in the powder X-ray diffraction pattern [d (in Å), I, (hkl)] are: 2.728, 100, (151); 2.513, 77, ($\bar 2$02); 3.079, 62, (310); 8.321, 60, (110); 3.421, 54, (131); 2.603, 42, (061); 2.175, 42, (261); 3.253, 41, (240); 2.969, 40, (221); 9.036, 40, (020).

Pink-orange crystals of a composition within the ferri-obertiite compositional space were found in vesicles in a pale beige silicate vein found from a basalt quarry at Mount Rothenberg, Eifel district, Germany. Associated minerals are potassic feldspar, alpha quartz paramorphic afterbeta quartz, eifelite (the second occurrence after the Caspar quarry at Bellerberg volcano, Eifel region), tridymite, rutile, roedderite and other amphiboles. The ideal formula of ferri-obertiite is ANaBNa2C(Mg3Fe3+Ti)TSi8O22WO2; the empirical formula derived for the holotype specimen from Mount Rothenberg from the results of electron-microprobe analysis and single-crystal structure refinement is A(Na0.76K0.22)∑0.98B(Na1.61Ca0.35Mn0.042+)∑2.00C(Mg3.58Mn0.112+Fe0.623+Ti0.664+Cr0.013+Zn0.01Ni0.01)∑5.00T(Si7.82Ti0.124+Al0.06)∑8.00O22W[O1.26F0.55(OH)0.19]∑2.00. The unit-cell dimensions are a = 9.7901(7), b = 17.9354(13), c = 5.2892(4)Å, β= 104.142(2)°, V = 900.58 (11) Å3. The space group is C2/m, Z = 2. Ferri-obertiite is biaxial (+), with α = 1.664, β = 1.680, γ = 1.722, all ±0.002 and 2V (meas.) = 66.4(3)o, 2V (calc.) = 64.7o.The strongest eight reflections in the powder X-ray pattern [d values (in Å), I, (hkl)] are: 2.704, 100, (151); 3.116, 76, (310); 3.388, 72, (131); 8.931, 72, (110); 2.529, 67, (202); 2.583, 39, (061); 2.160, 38, (261); 3.260, 37, (240). Both the mineral and thename have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2015-079); the rock specimen has been deposited at the Museo di Mineralogia, Dipartimento di Scienze della Terra e dell'Ambiente, Universitàdegli Studi di Pavia, under the code 2015-02.

To univocally identify mineral species on the basis of their formula, the IMA-CNMNC recommends the use of the dominant-valency rule and/or the site-total-charge approach, which can be considered two procedures complementary to each other for mineral identification. In this regard, several worked examples are provided in this study along with some simple suggestions for a more consistent terminology and a straightforward use of mineral formulae. IMA-CNMNC guidelines subordinate the mineral structure to the mineral chemistry in the hierarchical scheme adopted for classification. Indeed, a contradiction appears when we first classify mineral species to form classes (based on their chemistry) and subsequently we group together them to form supergroups (based on their structure topology): To date, more than half of recognized mineral supergroups include species with different anions or anionic complexes. This observation is in contrast to the current use of chemical composition as the distinguishing factor at the highest level of mineral classification.

High-temperature Fourier transform infrared (HT-FTIR) spectroscopy was used to characterize the deprotonation process of synthetic potassic-ferro-richterite of composition A ( K 0 . 90 Na 0 . 07 ) B ( Ca 0 . 54 Na 1 . 46 ) C ( Fe 4 . 22 2 + Fe 0 . 78 3 + ) T Si 8 O 22 W ( OH 1 . 70 O 0 . 30 2 − ) . Unpolarized single-crystal spectra were collected both in situ and on quenched samples, and heating experiments were conducted in air, at a rate of 10 °C/min. The room- T spectrum measured before annealing shows a main band at 3678 cm −1 and a minor band at 3622 cm −1 ; these are assigned to local configurations involving Fe 2+ at M (1) M (1) M (3) and facing a filled and an empty alkali-site, respectively. At 400 °C, a new band grows at 3656 cm −1 ; this is the most intense feature in the pattern at 450 °C. At T ≥ 500 °C, all peaks decrease drastically in intensity, and finally disappear at T > 600 °C. The total absorbance measured in situ increases significantly in the 25 T T range. This feature is consistent with an increase of the absorption coefficient (e) with T , the reason for which is still unclear. However, this feature has significant implications for the quantitative use of FTIR data in HT experiments. Examination of the relevant OH-stretching bands shows that iron oxidation occurs preferentially at the M (1,3) sites associated with occupied A sites. The deprotonation temperature indicated by FTIR for single-crystals is around 100 °C higher that that obtained by HT-X-ray diffraction (XRD) on single crystal by Oberti et al. (2016), whereas that obtained by HT-XRD on powders is intermediate. This unexpected observation can be explained by considering that: (1) the iron oxidation process, which is coupled to deprotonation and is probed by XRD, occurs preferentially at the crystal surface where it is triggered by the availability of atmospheric oxygen; (2) the proton diffusion, probed by FTIR, is slower that the electron diffusion probed by XRD; thus, the temperature shift may be explained by a much longer escape path for H in single-crystals than in powders. These results suggest that possible effects due to crystals size should be carefully considered in HT experiments done on Fe-rich silicates.

In order to characterize the role of Ti in the crystal structure of calcium amphiboles with high or even dominant oxo-component, the crystal structure of a Ti-rich calcium amphibole from a gabbro at Kaersut, Greenland, has been refined with single-crystal MoKα X-ray intensity data to an R 1(F) index of ~0.025, and with single-crystal Laue neutron intensity data to an R 1(F) index of ~0.053. The crystal used for X-ray structure refinement was characterized by electron- and ion-microprobe analysis. The site populations of the C-group cations Mg, Fe and Ti were calculated from the refined site-scattering values for the M(1), M(2) and M(3) sites derived by both X-ray and neutron diffraction. Ti is distributed among all the three sixfold coordinated M sites, with a strong preference for the M(1) and M(3) sites, where its main role is maintaining electroneutrality at the deprotonated O(3) site. The pattern of distortion of the M(1), M(2) and M(3) octahedra differs from that in F-free deprotonated or partly deprotonated amphiboles, where Ti4+ does not occur at the M(3) site. The neutron structure refinement provides also a clear picture of the environment of the proton, anisotropic displacement behaviour and potential hydrogen-bonding arrangements. A trifurcated hydrogen-bonding configuration has been identified, with two O(6) and one O(7) oxygen atoms as acceptors of weak hydrogen-bonds.

Oxo-mangano-leakeite, a newly approved end-member of the amphibole supergroup (IMA-CNMNC 20150-35), has been found in a rock containing manganese silicate and oxide at the Hoskins Mine, a Mn deposit 3 km west of Grenfell, New South Wales. The end-member formula of oxo-mangani-leakeite is ANaBNa2C(Mn3+4Li)TSi8 O22WO2, which would require SiO2 53.15, Mn2O3 34.91, Li2O 1.66, Na2O 10.28, total 100.00 wt.%. The empirical formula derived for the sample of this work from electron and ion microprobe analysis using constraints resulting from single-crystal structure refinement is A(Na0.65K0.36)∑ = 1.01B(Na1.94Ca0.06)∑ = 2.00C(Mg1.60Zn0.01 Li0.58)∑ = 5.01T(Si7.98Al0.02)∑ = 8.00O22W(O1.34OH0.66)∑ = 2.00. Oxo-mangano-leakeite is biaxial (–), with α = 1.681, β = 1.712, γ = 1.738, all ± 0.002, and 2V (meas.) = 81.0(4)°, 2V (calc.) = 83.5°. The unit-cell dimensions are a = 9.875(5), b = 17.873(9), c = 5.295(2) Å, β = 104.74(3)°, V = 903.8 (7) Å3; the space group is C2/m, with Z = 2. The strongest ten reflections in the powder X-ray pattern [d values (in Å), I, (hkl)] are: 8.423, 100, (110); 3.377, 46, (131); 4.461, 40, (040); 4.451, 40, (021); 3.134, 37, (310); 2.694, 37, (151); 2.282, 27, (); 2.734, 25, (31); 2.575, 24, (061); 2.331, 24, [() ()]. The holotype material is deposited in the Canadian Museum of Nature, Ottawa, under the catalogue number CMNMC 86895.

Microanalysis of Fe 3+ /∑Fe in geological samples using synchrotron-based X-ray absorption spectroscopy has become routine since the introduction of standards and model compounds. Existing calibrations commonly use least-squares linear combinations of pre-edge data from standard reference spectra with known coordination number and valence state acquired on powdered samples to avoid preferred orientation. However, application of these methods to single mineral grains is appropriate only for isometric minerals and limits their application to analysis of in situ grains in thin sections. In this work, a calibration suite developed by acquiring X-ray absorption near-edge spectroscopy (XANES) data from amphibole single crystals with the beam polarized along the major optical directions (X, Y, and Z) is employed. Seven different methods for predicting %Fe 3+ were employed based on (1) area-normalized pre-edge peak centroid, (2) the energy of the main absorption edge at the location where the normalized edge intensity has the highest R 2 correlation with Fe 3+ /∑Fe, (3) the ratio of spectral intensities at two energies determined by highest R 2 correlation with Fe 3+ /∑Fe, (4) use of the slope (first derivative) at every channel to select the best predictor channel, (5 and 6) partial least-squares models with variable and constant numbers of components, and (7) least absolute shrinkage and selection operator models. The latter three sophisticated multivariate analysis techniques for predicting Fe 3+ /∑Fe show significant improvements in accuracy over the former four types of univariate models. Fe 3+ /∑Fe can be measured in randomly oriented amphibole single crystals with an accuracy of ±5.5–6.2% absolute. Multivariate approaches demonstrate that for amphiboles main edge and EXAFS regions contain important features for predicting valence state. This suggests that in this mineral group, local structural changes accommodating site occupancy by Fe 3+ vs. Fe 2+ have a pronounced (and diagnostic) effect on the XAS spectra that can be reliably used to precisely constrain Fe 3+ /∑Fe.

Potassic-jeanlouisite, ideally K(NaCa)(Mg4Ti)Si8O22O2, is the first characterised species of oxo amphibole related to the sodium–calcium group, and derives from potassic richterite via the coupled exchange CMg–1W${\rm OH}_{{\rm \ndash 2}}^{\ndash}{} ^{\rm C}{\rm Ti}_1^{{\rm 4 +}} {} ^{\rm W}\!{\rm O}_2^{2\ndash} $. The mineral and the mineral name were approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification, IMA2018-050. Potassic-jeanlouisite was found in a specimen of leucite which is found in the lava layers, collected in the active gravel quarry on Zirkle Mesa, Leucite Hills, Wyoming, USA. It occurs as pale yellow to colourless acicular crystals in small vugs. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: A(K0.84Na0.16)Σ1.00B(Ca0.93Na1.02Mg0.04${\rm Mn}_{{\rm 0}{\rm. 01}}^{2 +} $)Σ2.00C(Mg3.85${\rm Fe}_{{\rm 0}{\rm. 16}}^{2 +} $Ni0.01${\rm Fe}_{{\rm 0}{\rm. 33}}^{3 +} {\rm V}_{{\rm 0}{\rm. 01}}^{3 +} $Ti0.65)Σ5.01T(Si7.76Al0.09Ti0.15)Σ8.00O22W[O1.53F0.47]Σ2.00. The holotype crystal is biaxial (–), with α = 1.674(2), β = 1.688(2), γ = 1.698(2), 2Vmeas. = 79(1)° and 2Vcalc. = 79.8°. The unit-cell parameters are a = 9.9372(10), b = 18.010(2), c = 5.2808(5) Å, β = 104.955(2)°, V = 913.1(2) Å3, Z = 2 and space group C2/m. The strongest eight reflections in the powder X-ray pattern [d values (in Å) (I) (hkl)] are: 2.703 (100) (151); 3.380 (87) (131); 2.541 (80) ($\bar 2$02); 3.151 (70) (310); 3.284 (68) (240); 8.472 (59) (110); 2.587 (52) (061); 2.945 (50) (221,$\bar 1$51).

We present in this paper the crystal-chemical (EMP analysis and single-crystal structure refinement, SREF) description of a sample of blue amphibole collected in 2012 in the Hydro quarry (neighbour to the Cappelen quarry) by one of the authors (KEL). According to the current IMA amphibole nomenclature (Hawthorne et al. 2012), it is classified as F-rich richterite.

We report polarized Raman spectra from potassic-magnesio-arfvedsonite in all informative scattering configurations. On the basis of the polarization selection rules, several A(g) vibrational modes have been identified. The B-g modes, however, are below the detection limits of the Raman spectrometer. The OH stretching band is situated between 3630 and 3750cm(-1), and its spectral shape is typical of amphiboles with high occupancy of the A site. It is composed of seven overlapping but resolvable subbands, which stem from occupied A-site configurations M(1)M(1)M(3)-OH-(A)(K/Na)-(OH)-O-W and M(1)M(1)M(3)-OH-(A)(K/Na)-F-W, as well as from vacant A-site configurations M(1)M(1)M(3)-OH-(A)-(OH)-O-W, with different Mg and Fe occupancy of the M(1) and M(3) sites. The experimental Raman spectra are compared with the results of theoretical calculations based on a shell-model force-field and a bond polarizability model. The simulated partial Raman spectra allowed us to assign many low-frequency Raman bands to stretching vibrations involving specific cation-oxygen bonds, as well as the higher-frequency modes of the Si-O skeleton. On the basis of our calculations we hypothesize that the Raman bands at 467, 540 and 589cm(-1) are related to a superposition of Fe-M(2)(3+)-O bond stretching and Si-O-Si bending vibrations.

Ferri-fluoro-katophorite is the second species characterised involving the rootname katophorite in the sodium–calcium subgroup of the amphibole supergroup. The mineral and its name were approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification, IMA2015-096. It was found in the Bear Lake diggings, Bancroft area, Ontario, Canada, where coarse euhedral crystals of amphibole, phlogopite, sanidine solid-solution (now coarsely exsolved to microcline perthite), titanite, augite, zircon and fluorapatite crystallised from a low-viscosity silicocarbonatitic magma of crustal origin. Greenish grey prismatic crystals of ferri-fluoro-katophorite generally protrude from the walls into a body of coarsely crystalline calcite, but they also occur away from the walls, completely enclosed by calcite. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: A(Na0.55K0.32)Σ0.87B(Na0.79Ca1.18Mn2+0.03)Σ2.00C(Mg3.29Mn2+0.02Fe2+1.19Fe3+0.31Al0.09Ti4+0.08Li0.02)Σ5.00T(Si7.39Al0.61)Σ8.00O22W[F1.23 (OH)0.77]Σ2.00. Ferri-fluoro-katophorite is biaxial (–), with α = 1.640(2), β = 1.652(2), γ = 1.658(2), 2Vmeas. = 68.9(2)° and 2Vcalc.. = 70.1°. The unit-cell parameters are a = 9.887(3), b = 18.023(9), c = 5.292(2) Å, β = 104.66(3)°, V = 912.3(6) Å3, Z = 2 and space group C2/m. The strongest ten lines in the powder X-ray pattern [d values (in Å) I (hkl)] are: 2.708, 100, (151); 2.388, 74, (131); 3.139, 72, (310); 8.449, 69, (110); 2.540, 65, ($\bar{2}$02); 2.591, 53, (061); 2.739, 47, ($\bar{3}$31); 2.165, 45, (261); 3.279, 44, ($\bar{2}$40); 2.341, 43, ($\bar{3}$51).

This short introduction aims to rethink the role of modern mineralogy and highlights the diverse and important contributions that it may provide in the study of materials and processes relevant to cultural heritage. It is argued that mineralogy lies in a very special position between Earth and materials sciences and that mineralogists have a profound perception of the structural and chemical complexity of natural materials. They possess knowledge of both the ancient and recent geological and physicochemical processes which produced the raw materials used by humans, and of the analogue processes used to transform them into artefacts. It is thus highly appropriate that a volume in the EMU series acknowledges some of the recent contributions of mineralogy to the investigation of human history, art and technology.

Natural garnets are robust silicate minerals stable over large ranges of temperature and pressure that can provide useful geochemical constraints on petrogenetic conditions. The purpose of this study is to determine how the size of cation sites controls rare earth elements (REE) incorporation in mantle eclogitic garnets. Major and lanthanide element data in a suite of mantle-derived eclogite garnets were combined with new single-crystal structure refinements (SREFs) to examine the effects of major-element chemistry and site dimension on the incorporation of REE into the garnet structure. Several distinct trends are apparent. Pyrope-rich samples similar to mantle lherzolitic garnets are enriched in the smaller heavy rare earth elements (HREE). Almandine-rich garnets are also HREE-enriched, but low rare earth elements (LREE) values are lower than in the pyrope-rich garnets. Intermediate garnet compositions are more depleted in HREE and enriched in LREE (Ce, Nd, and Sm). Finally, Ca-rich garnets (50% grossular component) are depleted in LREE and HREE, but are enriched in MREE. Hence, the X site dimension does exert a crucial role in REE incorporation into the garnet structure. Crystal structure refinements provide further evidence of this influence.

The chapters contributed to the volume recognize the important and diverse contributions of mineralogy to the valorization, characterization, interpretation and conservation of cultural heritage. The book focuses on examples of materials and methodological issues rather than technical/analytical details. We have attempted to deal with the cultural heritage materials in chronological order of their technological developments, to relate them to past human activities, and to highlight unresolved problems in need of investigation.

The complete mineral description of potassic-magnesio-arfvedsonite, a recently approved (IMA2016-083) new species of the amphibole supergroup is provided using electron microprobe analysis (EMPA), laser ablation inductively coupled plasma mass spectrometry, single-crystal structure refinement, Mössbauer and Raman spectroscopy, as well as measurement of optical and physical properties. The holotype material was found in syenitic and granitic dyke rocks in association with quartz, potassium feldspar and aegirine–augite from the Buhovo–Seslavtsi pluton, Bulgaria. Potassic-magnesio-arfvedsonite is monoclinic C2/m, with unit-cell parameters: a = 9.9804(11), b = 18.0127(19), c = 5.2971(6) Å, β = 104.341(2)° and V = 922.61 Å3. In transmitted plane-polarised light (λ = 590 cm–1), potassic-magnesio-arfvedsonite is pleochroic: X = yellow pale-green, Y = green and Z = dark-violet brown. It is biaxial (–), α = 1.645(2), β = 1.655(2), γ = 1.660(2) and 2Vmeas. = 60° and 2Vcalc. = 70°. The empirical unit formula obtained from EMPA and structure refinement is A(K0.86Na0.0.08)0.94B(Na1.74Ca0.25 Mn2+0.01)2.00C(Mg2.67Fe2+1.42Fe3+0.76Ti0.12Mn2+0.03)5.00TSi8O22W(OH1.58F0.22O0.20)2.00. The Fe3+/Fetot ratio (0.35) is consistent with both the Mössbauer spectra and the single-crystal structure refinement. The 10 strongest X-ray powder reflections [d values (in A°), I, (hkl)] are: 8.519, 80.5, (110); 3.402, 67.3, (131); 3.295, 41.0, (240); 3.173, 65.0, (310); 2.752, 35.6, ($\bar{3}$31); 2.715, 100.0 (151); 2.591, 44.1, (061); 2.542, 73.2, ($\bar{2}$02); 2.348, 38.5, ($\bar{3}$51); 2.174, 42.0, (261). Potassic-magnesio-arfvedsonite is the product of strongly peralkaline and potassic (perpotassic) magma compositions. Trace-element analysis shows that this amphibole did not exert significant control on trace-element distribution in the crystallising peralkaline magma.

The high-temperature behavior of synthetic potassic-ferro-richterite was addressed to obtain data relevant to understanding petrogenetic processes as well as to testing complementarity and mutual calibration of single-crystal X-ray diffraction (XRD) analysis plus structure refinement (SREF) with single-crystal FTIR spectroscopy. This experimental approach aims at: (1) better quantifying the onset of deprotonation, its development and the amount, if any, of relict OH at the end of the process; (2) verifying whether or not the process is homogeneous within the crystal; and (3) evaluating local changes in cation environments close to the OH dipole. In this first part of a series of two papers, we report on the crystal-chemical characterization of potassic-ferro-richterite and on a single-crystal XRD study at high T . Detailed analysis of the available data allowed us to obtain a full characterization of the bulk and crystal chemistry of the studied crystal, hence improving the unit formula suggested by Redhammer & Roth (2002). In operando H T measurements up to 1073 K showed quite anomalous behavior with respect to pargasite/kaersutites, specifically a much lower T for the onset of the deprotonation process (around 500 K), and strongly anomalous behavior of the β angle, which shows inverse slopes for protonated and deprotonated phases. “Oxo-potassic-ferro-richterite” is formed upon deprotonation and remains stable at least up to 1073 K under the conditions of this study. Structure refinements from data collected at different temperatures allowed us to detect changes in the crystal-structure geometry and in turn to decipher the way in which amphiboles with such a peculiar composition respond to increasing T and deprotonation. The thermal expansivity coefficients α (×10 −5 K −1 ) are: potassic-ferro-richterite: α a = 1.30(6), α b = 0.93(6), α c = 0.12(3), α β = −0.49(5), α asinβ = 1.34(8), α V = 2.59(2); “oxo-potassic-ferro-richterite”: α a = 1.71 (3), α b = 0.97(1), α c = 0.193(8), α β = 0.22(1), α asinβ = 1.59(4), α V = 2.74(2).

Following the characterization of the new amphibole species fluoro-leakeite, ideally ANa BNa2 C(Mg2Al2Li) TSi8 O22 WF2, at Norra Karr (Sweden), so far considered the type locality of eckermannite, re-examination of the holotype material of eckermannite deposited at the Museum of Natural History in London (BM 1949.151) and of the original sample analyzed by Tornebohm (1906) confirmed that they both are actually fluoro-leakeite. A survey of literature data showed that the only analysis reported for eckermannite is that of sample AMNH 108401 from the Jade Mine Tract, Myanmar. Complete characterization of that sample has led to the approval of a new holotype for eckermannite (IMA-CNMNC 2013-136), ideally ANa BNa2 C(Mg4Al) TSi8 O22 W(OH)2, which is described in this work. Holotype eckermannite from Myanmar has the empirical unit formula A(Na0.87K0.06)∑=0.93 B(Na1.89Ca0.11)∑=2.00 C(Mg3.87Fe2+0.09Mn0.01Fe3+0.38Al0.62)∑=4.97 TSi8.00 O22 W(F0.03OH1.97)∑=2.00. It is monoclinic, C 2/ m , with a = 9.8087(7), b = 17.8448(13), c = 5.2905(4) A, β = 103.660(1), V = 899.8(1) A3; Z = 2, D calc = 3.02 g/cm3. Optics: biaxial (−); α = 1.605, β = 1.630, γ = 1.634 all ±0.002 (λ = 590 nm). The 10 strongest reflections in the X-ray powder pattern [ d values (in A), I , ( hkl )] are: 2.702, 100, [(331) (151)]; 3.395, 59, (131); 3.128, 56, (310); 2.525, 56, (202); 8.407, 42, (110); 2.574, 36, [(061) (002)]; 3.257, 34, (240); 2.161, 33, (261); 2.966, 33, (060); 4.460, 30, (040). The reason for the rarity of eckermannite compositions are examined and discussed based on considerations on the short-range order of A cations and W anions.

The crystal-chemical characterization of an amphibole with an unusual composition, A(Na0.76K0.24)B(Ca1.42Na0.56Mn2+0.02)C(Mg2.64Fe2+1.95Mn2+0.07Mg2.64Zn0.01Fe3+ 0.01Ti4+ 0.32)T(Si7.18Al0.82)O22 W[(OH)0.58O0.27F1.15], found in pegmatitic veins at Kariåsen, Larvik Plutonic Complex, Norway, provides an excellent example of the detection and estimation of the oxo component in amphibole. The use of Ti as a proxy for the oxo component is discussed and a procedure to derive accurate Ti partitioning from the results of structure refinement is described. Because the presence and amount of oxo component in amphiboles are important in order to determine values of fO2 and fH2O, especially in igneous and magmatic systems, this procedure should be applied any time the compositional data or the petrological context indicate the presence of significant Ti, or suggest that the oxo component may be a relevant issue.

During systematic characterization of amphiboles that still lack a complete mineral description, fluoro-tremolite was identified in a specimen from the Limecrest-Southdown quarry, Sparta, New Jersey, USA, which was provided by the Franklin Mineral Museum. The ideal formula of fluoro-tremolite isA□BCa2CMg5TSi8O22WF2and the empirical formula derived for the holotype specimen, based on the results of electron-microprobe analysis and single-crystal structure refinement, isA(Na0.28K0.02)Σ0.30B(Ca1.99Na0.01)Σ2.00C(Mg4.70${\rm Fe}_{{\rm 0}{\rm. 28}}^{{\rm 2 +}} $Zn0.01${\rm Ti}_{{\rm 0}{\rm. 01}}^{{\rm 4 +}} $)Σ5.00T(Si7.68Al0.32)Σ8.00O22W(F1.16OH0.84)Σ2.00.The unit-cell dimensions in space groupC2/marea= 9.846(2),b= 18.050(3),c= 5.2769(14) Å, β = 104.80(2)° andV= 906.7 (3) Å3andZ= 2; thea:b:cratio is 0.545:1:0.292. Fluoro-tremolite is biaxial (+), with α = 1.5987(5), β = 1.6102(5), γ = 1.6257(5), 2V(meas.) = 85(1)oand 2V(calc.) = 82o. The strongest ten reflections in the powder X-ray pattern [dvalues (in Å),I, (hkl)] are: 2.706, 100, (151); 3.126, 67, (310); 2.531, 59, ($\bar 2$02); 3.381, 57, (131); 2.940, 43, ($\bar 1$51, 221); 3.276, 37, (240); 2.337, 36, ($\bar 3$51); 2.592, 35, (061); 2.731, 34, ($\bar 3$31); 2.163, 34, (261). Both the mineral and the mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2016–018); the holotype has been deposited at the Franklin Mineral Museum (32 Evans Street, Franklin, 07416 New Jersey, US), under the catalogue number 7710.Comparison with new data on tremolite and synthetic fluoro-tremolite provides a more sound crystal-chemical model of the end-member compositions and their solid-solution.

In this work, we investigate the oxidation behavior of a nearly end-member riebeckite, ideally Na-2(Fe32+Fe23+)Si8O22(OH)(2), by using vibrational FTIR and Raman spectroscopies. Combining these results with previous studies performed on the same sample by single-crystal structure refinement and Mossbauer spectroscopy, we conclude that iron oxidation in riebeckite is a multi-step process. (1) In the similar to 523 K < T < 623 K temperature range, the O-H bond lengthens and both the electrons and the hydrogen cations delocalize. Raman analysis shows that this step is reversible upon cooling to room temperature. (2) In the 623 K < T < 723 K range, the kinetic energy increases so that the electrons can be ejected from the crystal; beyond 723 K an irreversible oxidation of Fe occurs that couples with irreversible changes in the SiO4 double-chains leading to a contraction of the unit-cell volume, i.e., to structural changes detectable at the long-range scale. (3) Beyond 823 K, the irreversible oxidation is completed and H+ ions are forced to leave the crystal bulk. Because of this multi-step process, the onset of the deprotonation process is detected at similar to 700 K by single-crystal XRD analysis of the unit-cell parameters, but starts at 623 K as indicated by Mossbauer spectroscopy on powders (and by changes in the cation distribution observed by structure refinement). Also, Raman scattering shows that the release of H+ from the crystal surface starts similar to 100 K before the complete deprotonation of the crystal bulk is witnessed by FTIR absorption. Hence, the oxidation of Fe starts at the crystal surface and induces electron and H+ migration from the crystal interior to the rim and thus subsequent oxidation through the crystal bulk. No deprotonation is observed by FTIR either in powders embedded in KBr or in crystals heated in N-2 atmosphere, implying that the release of H+ needs surficial (atmospheric) oxygen to form H2O molecules. Fe2+-> Fe3+ oxidation produces a flux of electrons throughout the crystal matrix, which generates electrical conductivity across the amphibole. An important implication of this work, which might have interesting applications in material science, is that iron oxidation in riebeckite (and possibly in other Fe-rich silicates) is reversible in a given range of temperature. Also, this work shows that complex processes cannot be fully understood or even monitored accurately without using a proper combination of independent techniques.

[The HT behaviour of a well-characterized sample of riebeckite has been examined by combining X-ray diffraction, FTIR and Mössbauer spectroscopy. The crystal-chemical composition of the crystal studied is: A(K0.05Na0.04) B(Na1.86Ca0.09Fe2+0.05) C(Fe2+2.94Mg2+0.22Mn2+0.02Zn2+0.01Fe3+1.74Al3+0.06Ti4+0.01) T(Si7.95Al0.05) O22 W(OH1.9F-0.10). The onset of the deprotonation process is detected at ?700 K by single-crystal XRD analysis of the unit-cell parameters, but starts at 623 K as indicated by Mössbauer spectroscopy on powders (and by changes in the cation distribution observed by structure refinement). FTIR analysis shows that a completely deprotonated oxo-amphibole is obtained after annealing at 893 K. Room-T single-crystal structure refinements of the deprotonated phase shows a very peculiar cation disorder, which has never been observed in amphiboles until now: there is significant depletion of B and C cations coupled with an increase in A cations, which implies the presence of vacancies at the M(3) and the M(4) sites in double-chain silicates. FTIR data collected at 873 K confirm both this conclusion and the onset of the cation exchange before completion of deprotonation. Axial and volume thermal expansion coefficients were determined in the T range 298-698 K for riebeckite (?a = 1.40(2)·10-5 K-1, ?b = 0.67(1)·10-5 K-1, ?c = 0.17(2)·10-5 K-1, ?? = -0.07(1)·10-5 K-1and ?V = 2.27(2)·10-5 K-1) and in the 298-1173K range for the oxo-amphibole (?a = 1.53(2)·10-5 K-1, ?b = 0.77(1)·10-5 K-1, ?c = 0.25(1)·10-5 K-1, ?? = 0.10(1)·10-5 K-1and ?V = 2.52(2)·10-5 K-1). object Object]

In this work, we have studied the relationships between mass concentration and unit formula of amphibole using 114 carefully selected high-quality experimental data, obtained by electron microprobe (EMP) + single-crystal X-ray structure refinement (SREF) +/- secondary-ion mass spectrometry (SIMS) analyses, of natural and synthetic Li-free monoclinic species belonging to the Ca and Na-Ca subgroups, and 75 Li-free and Mn-free C2/m end-members including oxo analogs of Ca amphiboles. Theoretical considerations and crystal-chemical driven regression analysis allowed us to obtain several equations that can be used to: (1) calculate from EMP analyses amphibole unit-formulas consistent with SREF +/- SIMS data, (2) discard unreliable EMP analyses, and (3) estimate O-W(2-) and Fe3+ contents in Li-free C2/m amphiboles with relatively low Cl contents (

In order to clarify details of volatiles incorporation in arrojadites, two samples p\reviously characterized by X-ray diffraction and electron-microprobe (EMP) and LA-ICPMS analysis were investigated by single-crystal FTIR spectroscopy. The present study confirms and makes more quantitative previous results by single-crystal structure refinement about the presence and orientation of three OH − groups (one with partial occupancy) in the arrojadite structure. The FTIR spectra showed the presence of NH 4 + in arrojadite from Yukon, which was confirmed by EMP analysis ( ca . 700 ppm N). Micro FTIR imaging was used to check the homogeneity of OH and NH 4 + across the examined samples, as a prerequisite for the single-crystal polarized study. Based on the hydrogen bonding environment determined by structure refinement, the bands observed in the 3600–3500 cm −1 region can be assigned to the OH1 (at lower frequency) and OH2 (at higher frequency) dipoles. In the spectrum of arrojadite from Yukon several hyperfine components are resolved; these can be assigned to local Mg/ Fe 2+ octahedral configurations at the OH-coordinated octahedra. Both spectra show a very broad absorption extending from ~ 3500 to 2500 cm −1 which is assigned to the OH3 hydroxyl group. The orientation of the O-H dipoles calculated from the FTIR absorbance data are in excellent agreement with those calculated from the refined atomic coordinates, confirming the validity of the latter method also in the case of low-Z elements. Assuming the water content derived from EMP analysis, an integrated molar coefficient (polarized data) ɛ I = 63937 l/(mol□cm −2 ) is calculated for the spectroscopic quantification of H 2 O in arrojadite. For N, based on the EMP analysis, we obtain (for unpolarized data in the N-O bending region) ɛ i = 11000 ± 2000 l/(mol□cm −2 ) and ɛ I = 300 ± 60 l/(mol□cm −1 ) from integrated and linear intensity data, respectively.

In the paper on which we are commenting ([Joy & Evans 2014][1]), the authors (hereafter referred to as J&E) introduced a new mineral belonging to the amphibole supergroup, gave it a name, and discussed its relations with coexisting amphiboles and amphiboles reported in previous literature. First

New chemical (EMP, SIMS) and structural data are reported for a suite of crystals of oxo-mangani-leakeite and mangano-mangani-ungarettiite from their common type locality, the Hoskins mine (New South Wales, Australia). Notwithstanding the low OH content, FTIR analysis of selected sampleshas provided considerable information on short-range order in these Mn3+-rich amphiboles, and shows that Li is associated with occupied A sites and is linked to the oxo-component at the O(3) site. Comparative analysis of all available data allows us to: (1) further improveour understanding of the crystal-chemistry of these very peculiar compositions of the oxo-amphibole group; and (2) calculate reliable site-populations. The proposed limited compositional variability has been confirmed. The two amphiboles have completely different arrangements of CR3+cations. In oxo-mangani-leakeites, those CR3+ cations related to the oxocomponent occur at the M (1) site, whereas those CR3+ cations related to the leakeite charge-arrangement occur at the M (2) site. In mangano-mangani-ungarettiite,all CR3+ cations order at the M (1) and M (3) sites, and local bond-valence requirements are satisfied by the presence of Mn3+, which assumes a strongly distorted coordination due to its degenerate eg electronic state. Therefore,the inverse patterns observed for both cation-ordering and deformation of the octahedra are incompatible with solid-solution between these two species that coexist at the Hoskins mine.

Magnesio-riebeckite from the dumps of the abandoned mine of Varenche (45°47’22’’ N, 7°29’17’’ E), Saint-Barthélemy, Nus, Aosta Valley (Italy), was studied to provide the complete mineral description (including crystal structure) and insights into the crystal-chemistry of riebeckite. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is A(Na0.09K0.01)Σ=0.10B(Na1.77Ca0.11Mg0.08Mn2+ 0:04)Σ=2.00C(Mg2.93Mn2+0:13Fe2+0:07Zn0.01Ni0.12Fe3+1:25Al0.48Ti0.01)Σ=5.00T(Si7.92Al0.08)Σ=8.00 O22W(OH1.88F0.12)Σ=2.00. Magnesio-riebeckite is biaxial (+), with α = 1.678(2), β = 1.682(2), γ = 1.688(2) and 2V (meas.) = 80.2(1.7)°, 2V (calc.) = 78.7°. The unit-cell parameters are a = 9.6481(14), b = 17.873(3), c = 5.3013(7) Å, β = 103.630(2)°, V = 888.4 (2)Å3, Z = 2, space group C2/m. The strongest ten reflections in the powder X-ray pattern [d values (in Å), I, (hkl)] are: 2.701, 100, (151); 8.303, 83, (110); 3.079, 62, (310); 3.391, 53, (131); 4.467, 50, (040,021); 2.522, 50, (̅202); 2.578, 35, (061); 2.155, 30, (261), 4.855, 30, (̅111), 2.300, 29, (̅351).

Davidsmithite, a newly approved feldspathoid mineral (IMA 2016-070), occurs as a rock-forming mineral in the Liset eclogite pod (Norwegian Caledonides). It is transparent, colourless, uniaxial negative, omega = 1.538(2), epsilon = 1.535(2). No cleavage was observed. Davidsmithite is hexagonal, space group P6(3) and has unit-cell dimensions: a = 9.982(1) angstrom ; c = 8.364(2) angstrom ; V = 721.74 angstrom(3); Z = 1; the c: a ratio is 0.8379; the calculated density is 2.597 g cm(-3). The approved electron-microprobe analysis gave the crystal-chemical formula: ([Ca-0.636 square(0.636)]square 0.414K0.165Na0.149)(Sigma 2.000)Na-6.000(Al7.863Fe0.0193+)Sigma 7.882Si8.192O32 (where square = vacancy). Davidsmithite completes the compositional space of the nepheline-structure group by providing a new root-composition, (Ca square)(2)Na6Al8Si8O32. It is the Ca-analogue of classical nepheline, to which it is related by the heterovalent substitution of K-2(+) by [Ca2+square.]. Most of the Ca2+ ions are situated in the same atomic position as K+ in nepheline, but some occur in a new and disordered (Ca) atomic position, whose centre is shifted by 2.18 angstrom along the 6-fold axis. The studied samples show some solid-solution towards the other two possible end-members of the nepheline compositional space, so that the channel site contains all of Ca and K in the unit formula, with some Na and square. In the Liset eclogite pod, davidsmithite occurs in retrogressed, formerly jadeite-rich zones; it commonly overgrows lisetite and is associated with albitic plagioclase and taramitic amphibole. This eclogite occurrence is noted for its bulk-rock compositions rich in (Na+Al) and poor in (K+Mg). The paucity in K prevented the growth of nepheline, and the paucity in Si in precursor jadeite led to the growth of a feldspathoid (davidsmithite) as well as of lisetite; a feldspar (albite or oligoclase) also occurs nearby.

A new classification and nomenclature scheme for the amphibole-supergroup minerals is described, based on the general formula AB 2 C 5 T 8 O 22 W 2 , where A = □, Na, K, Ca, Pb, Li; B = Na, Ca, Mn 2+ , Fe 2+ , Mg, Li; C = Mg, Fe 2+ , Mn 2+ , Al, Fe 3+ , Mn 3+ , Ti 4+ , Li; T = Si, Al, Ti 4+ , Be; W = (OH), F, Cl, O 2− . Distinct arrangements of formal charges at the sites (or groups of sites) in the amphibole structure warrant distinct root names , and are, by implication, distinct species; for a specific root name, different homovalent cations (e.g., Mg vs. Fe 2+ ) or anions (e.g., OH vs. F) are indicated by prefixes (e.g., ferro-, fluoro-). The classification is based on the A, B, and C groups of cations and the W group of anions, as these groups show the maximum compositional variability in the amphibole structure. The amphibole supergroup is divided into two groups according to the dominant W species: W (OH,F,Cl)-dominant amphiboles and W O-dominant amphiboles (oxo-amphiboles). Amphiboles with (OH, F, Cl) dominant at W are divided into eight subgroups according to the dominant charge-arrangements and type of B-group cations: magnesium-iron-manganese amphiboles, calcium amphiboles, sodium-calcium amphiboles, sodium amphiboles, lithium amphiboles, sodium-(magnesium-iron-manganese) amphiboles, lithium-(magnesium-iron-manganese) amphiboles and lithium-calcium amphiboles. Within each of these subgroups, the A- and C-group cations are used to assign specific names to specific compositional ranges and root compositions. Root names are assigned to distinct arrangements of formal charges at the sites, and prefixes are assigned to describe homovalent variation in the dominant ion of the root composition. For amphiboles with O dominant at W, distinct root-compositions are currently known for four (calcium and sodium) amphiboles, and homovalent variation in the dominant cation is handled as for the W (OH,F,Cl)-dominant amphiboles. With this classification, we attempt to recognize the concerns of each constituent community interested in amphiboles and incorporate these into this classification scheme. Where such concerns conflict, we have attempted to act in accord with the more important concerns of each community.

The thermoelastic behaviour of a natural gedrite having the crystal-chemical formula ANa0.47 B(Na0.03 Mg1.05 Fe 0.86 2+ Mn0.02 Ca0.04) C(Mg3.44 Fe 0.36 2+ Al1.15 Ti 0.05 4+ ) T(Si6.31 Al1.69)O22 W(OH)2 has been studied by single-crystal X-ray diffraction to 973 K (Stage 1). After data collection at 973 K, the crystal was heated to 1,173 K to induce dehydrogenation, which was registered by significant changes in unit-cell parameters, M1–O3 and M3–O3 bond lengths and refined site-scattering values of M1 and M4 sites. These changes and the crystal-chemical formula calculated from structure refinement show that all Fe2+ originally at M4 migrates into the ribbon of octahedrally coordinated sites, where most of it oxidises to Fe3+, and there is a corresponding exchange of Mg from the ribbon into M4. The resulting composition is that of an oxo-gedrite with an inferred crystal-chemical formula ANa0.47 B(Na0.03 Mg1.93 Ca0.04) C(Mg2.56 Mn 0.02 2+ Fe 0.10 2+ Fe 1.22 3+ Al1.15 Ti 0.05 4+ ) T(Si6.31 Al1.69) O22 W[O 1.12 2− (OH)0.88]. This marked redistribution of Mg and Fe is interpreted as being driven by rapid dehydrogenation at the H3A and H3B sites, such that all available Fe in the structure orders at M1 and M3 sites and is oxidised to Fe3+. Thermoelastic data are reported for gedrite and oxo-gedrite; the latter was measured during cooling from 1,173 to 298 K (Stage 2) and checked after further heating to 1,273 K (Stage 3). The thermoelastic properties of gedrite and oxo-gedrite are compared with each other and those of anthophyllite.

The thermoelastic behaviour of anthophyllite has been determined for a natural crystal with crystal-chemical formula ANa0.01 B(Mg1.30Mn0.57Ca0.09Na0.04) C(Mg4.95Fe0.02Al0.03) T(Si8.00)O22 W(OH)2 using single-crystal X-ray diffraction to 973 K. The best model for fitting the thermal expansion data is that of Berman (J Petrol 29:445–522, 1988) in which the coefficient of volume thermal expansion varies linearly with T as α V,T = a 1 + 2a 2 (T − T 0): α298 = a 1 = 3.40(6) × 10−5 K−1, a 2 = 5.1(1.0) × 10−9 K−2. The corresponding axial thermal expansion coefficients for this linear model are: α a ,298 = 1.21(2) × 10−5 K−1, a 2,a = 5.2(4) × 10−9 K−2; α b ,298 = 9.2(1) × 10−6 K−1, a 2,b = 7(2) × 10−10 K−2. α c ,298 = 1.26(3) × 10−5 K−1, a 2,c = 1.3(6) × 10−9 K−2. The thermoelastic behaviour of anthophyllite differs from that of most monoclinic (C2/m) amphiboles: (a) the e 1 − e 2 plane of the unit-strain ellipsoid, which is normal to b in anthophyllite but usually at a high angle to c in monoclinic amphiboles; (b) the strain components are e 1 ≫ e 2 > e 3 in anthophyllite, but e 1 ~ e 2 ≫ e 3 in monoclinic amphiboles. The strain behaviour of anthophyllite is similar to that of synthetic C2/m ANa B(LiMg) CMg5 TSi8 O22 W(OH)2, suggesting that high contents of small cations at the B-site may be primarily responsible for the much higher thermal expansion ⊥(100). Refined values for site-scattering at M4 decrease from 31.64 epfu at 298 K to 30.81 epfu at 973 K, which couples with similar increases of those of M1 and M2 sites. These changes in site scattering are interpreted in terms of Mn ↔ Mg exchange involving M1,2 ↔ M4, which was first detected at 673 K.

Potassic-aluminotaramite, ideally A K (CaNa) B (Fe 3 2+ Al 2 ) C (Si 6 Al 2 ) O 22 W (OH) 2 , has been found in a meta-monzonite rock sampled at Sierra de los Filabres, S.E. Spain; the paragenesis that contains the amphibole is mainly formed by feldspar, quartz, and clinopyroxene. This paper reports a complete mineral description and crystal-structure details for this new taramite end-member that has been recognised by IMA-CNMMC with the vote 2007-015. Holotype potassic-aluminotaramite has the experimental unit formula A (Na 0.34 K 0.66 ) ∑1.00 B (Fe 0.01 2+ Na 0.85 Ca 1.14 ) ∑2.00 C (Fe 2.80 2+ Mg 0.33 Al 1.26 Fe 0.46 3+ Ti 0.05 Mn 0.10 ) ∑5.00 T (Si 6.01 Al 1.99 ) ∑8.00 O 22 W (OH 1.96 F 0.03 Cl 0.01 ) ∑2.00 ; a = 9.8505(5), b = 18.0075(9), c = 5.3518(3) A, β = 104.775(4), V = 917.9(2) A 3 ; D calc = 3.40 g/cm 3 . Optics: biaxial (−); α 1.686(1), β 1.703(3), γ 1.706(3) (λ = 589 nm). The ten strongest reflections in the X-ray powder pattern [ d values (in A), I , ( hkl )] are: 8.420, 100, (110); 2.714, 75.03, (151); 2.565, 59.62, (−202); 3.127, 52.54, (310); 2.596, 49.03, (061); 3.400, 37.92, [(131) (041)]; 2.166, 33.71, [(261) (−332)]; 2.340, 32.38, (−351); 2.956, 24.79, (221); 2.297, 24.57, [(−171) (−312)].

This paper describes a multi-technique approach to the complete crystal-chemical characterization of a gadolinite-(Y) sample found in a volcanic holocrystalline ejectum near the Vico lake (Latium, Italy). Gadolinite-(Y) occurs as poly-twinned crystals forming rounded short-prismatic aggregates (generally 0.1-0.3 mm in size, with the largest ever found >1 mm), associated with zircon, thorite, danburite, betafite, and tourmaline. Both the chemical and the structural characterization of gadolinite-(Y) from Vico required nonstandard procedures. After correction for (100) twinning, the structure of a crystal with unit-cell dimensions a = 4.7708(4) angstrom, b = 7.6229(7) angstrom, c = 9.8975(9) angstrom, beta = 90.017(7)degrees, and V= 359.95(6)angstrom(3) was refined in the P2(1)/c space group down to R = 2.3%. Electron microprobe (EMP) analyses failed to give accurate quantification of major elements, due to the presence of light and volatile elements as well as of rare earth elements (REE) and actinides. Secondary ion-mass spectrometry (SIMS) analysis done with accurate calibrations on well-characterized minerals allowed quantification of light, volatile, REE, and actinide elements, and also of Ca and Si. The derived chemical composition was interpreted with reference to the site-scattering values obtained from single-crystal structure refinement. The resulting unit formula is (Ca0.81REE0.66Y0.39Th0.13U0.02)(Sigma 2.01)(Fe0.292+Li0.14 Fe0.123+Mn0.02Mg0.01)(Sigma 0.58)(Si1.98Be1.09B0.81Li0.12)(Sigma 4.00) O-8(O1.20F0.51OH0.29)(Sigma 2.00,) which yields a calculated density of 4.267 g cm(-3). Fourier transform infrared spectroscopy (FTIR) single-crystal spectrum of gadolinite-(Y) shows several absorptions in the OH-stretching region that can be assigned to the different local configurations involving Ca and (REE,Y) at the A site and Be, B, and Li at the Z site. Lithium incorporation in gadolinite-group minerals is proposed to occur according to the exchange vectors: (1) Fe-x(2+) + Y-A -> Li-x + (A)(Th + U) and (2) Be-z + Fe-x(2+) -> Li-z + Fe-x(3+); the maximum amount of Li allowed in the gadolinite structure is 1.0 apfu. This work provides the first evidence that Li is a significant component in gadolinite-group minerals, particularly in geochemical environments enriched in actinides. This conclusion suggests that materials having the composition of Li-rich gadolinite may be considered as possible forms for radioactive waste disposal.

The P21/m ↔ C2/m displacive phase transition has been studied on a synthetic amphibole with unit formula ANa0.90 B(Na0.92Mg1.08)C(Mg4.98V0.02)TSi8O22 O3F2. The evolution of the unit-cell parameters and of the intensities of a set of super-lattice reflections was monitored in the T range 100–944 K. Polynomial fitting of a 24 Landau potential to the evolution of the order parameter with T yielded a critical temperature (T c) of 395 ± 5 K (398 ± 6 when considering low-T saturation of the order parameter), and Landau coefficients compatible with second-order transition. The values of T c and the coefficients for the phase transition obtained in this work are compared to those previously obtained for synthetic ANa0.83 B(Na0.83Mg1.17)CMg5 TSi8O22 O3(OH)2 and to other data available in the literature. The substitution of OH by F at the O(3) site does not change the character of the transition, but decreases the T c by at least 132 K, showing that the size of the M(4) polyhedron is not the only significant factor, and that the size of the octahedra and/or their different thermal expansion also play a role. Single-crystal structure refinements done at 100, 160, 220, 280, 340, 406, 514, 621, 729, 836 and 944 K allowed monitoring the changes in the structure and in the shape of electron density, which occur approaching the transition and during further heating. Mean thermal expansion coefficients for the different polyhedra in the structure were calculated for the high-T C2/m phase, and are compared with those of other amphiboles with 5 Mg atoms per formula unit at the C-sites. The presence of F significantly affects both cation ordering within the A cavity and the thermal expansion along the b and c edges.

Magnesio-ferri-fluoro-hornblende has the ideal formula A□B Ca2C(Mg4Fe3+)T(Si7Al)O22WF2(Hawthorne et al., 2012). The holotype sample described in this work occurs as prismatic crystals in vugs of volcanic rocks (Seruci ignimbrites), found along the coast road ∼5.5 km northeast of Portoscuso, Cagliari, Sardinia; associated minerals are tridymite, todorokite, magnetite, and hematite. The name and the mineral were approved by the IMA CNMNC (2014-091). Holotype magnesio-ferri-fluoro-hornblende is monoclinic, space group C2/m, a = 9.839(5), b = 18.078(9), c = 5.319(3) Å, β = 104.99(3)°, V = 913.9(9) Å3, Z = 2. The density calculated from the empirical formula is 3.315 g cm–3. In plane-polarized light, magnesio-ferri-fluoro-hornblende is pleochroic, X = pale grey (least), Y = dark grey (most), Z = pale brownish grey (intermediate); X^a= 47.6° (β obtuse), Y // b, Z^c= 33.4° (β acute). It is biaxial negative, α = 1.669, β = 1.676, γ = 1.678, all ±0.002; 2Vobs= 74(1)°, 2Vcalc= 56°. The strongest eight lines in the powder X-ray diffraction pattern are [d in Å (I)(hkl)]: 2.711 (100)(151), 8.412 (89)(110), 3.121 (64)(310), 2.553 (61)(2̄02), 3.389 (55)(131), 2.599 (45)(061), 2.164 (36)(261), and 2.738 (34)(3̄31). Electron-microprobe analysis of the refined crystal gave SiO245.34, Al2O36.18, TiO21.22, FeO 15.24, Fe2O36.27, MgO 9.71, MnO 0.78, ZnO 0.06, CaO 10.18, Na2O 1.35, K2O 1.15, F 3.22, Cl 0.30, H2Ocalc 0.37, sum 99.95 wt.%. The empirical formula unit, calculated on the basis of 24 (O, OH, F, Cl) apfu with (OH + F + Cl) = 2 apfu is: (Na0.15K0.22)∑0.37(Na0.25Ca1.66Mn0.09)∑2.00(Mg2.20Fe2+1.94Mn0.01Zn0.01Fe3+0.72Ti0.13)∑5.01(Al1.11Si6.89)∑8.00O22[F1.55(OH)0.37Cl0.08)∑2.00.

Amphiboles were crystallized in sub-liquidus experiments at 0.5–2.0 GPa and 1000–1050 °C from hydrous nepheline basanite and olivine basalt starting compositions. The amphiboles and coexisting (quenched) melts were analysed for major, minor and trace elements by a combination of electron microprobe, laser ablation microprobe and inductively-coupled plasma mass-spectrometry (LAM ICP-MS). Individual amphiboles were also characterized by single-crystal X-ray structure refinement, and empirical estimates of dehydrogenation were obtained based on M1–M2 distances. The amphiboles display compositional variation that can be interpreted as crystal-chemical responses to: (1) increasing pressure, and (2) changes in oxygen fugacity ( f O 2 ) and the activity of H 2 O. As pressure increases, Al moves from the T1 tetrahedron (where it is replaced by Si) to the octahedral M2 site. This coupled substitution, which implies an increase in coordination number for Al, results in a decrease in the c and b unit-cell edges. The overall decrease in unit-cell volumes is kept small, however, by an increase in the B (Fe, Mg) content with increasing pressure, which in turn decreases the volume occupied by the B-cations but increases the sin β value. In this way, the entrance of minor K at the A site and Cl at the O3 site (K D s for both increase with pressure) is allowed, resulting in a slight lengthening of the a edge. The degree of dehydrogenation at O3 correlates inversely with the H 2 O concentration in coexisting melts. Generally, dehydrogenation is locally balanced by M1 Ti, with the Ti excess with respect to ½ O 2− ordered at the M2 site. In one sample, crystallized under more oxidizing conditions, O 2− is > 2Ti, and local charge balance requires the presence of Fe 3+ ordered at the M1 (and M3) sites. D amph/melt values measured for the high field strength elements Ti, Zr, Hf, Nb and Ta ( D HFSE ) correlate positively with O 2− and with [4] Al, suggesting that Ti, Zr, Hf, Nb and Ta (HFSE) are incorporated in both the M1 and the M2 sites. Partition coefficients for rare earth elements ( D REE ) correlate positively with [4] Al and negatively with [6] Al. Increased f O 2 results in increased Fe 3+ , [4] Al and D REE , but does not produce a noticeable increase in O 2 − or in D HFSE .

Here we present 45 Sc and 27 Al NMR results on Sc-doped pyrope (Mg 3 Al 2 Si 3 O 12 ), grossular (Ca 3 Al 2 Si 3 O 12 ), and an 80% grossular-20% pyrope garnet (grs80) that have recently been well-studied by X-ray diffraction and X-ray spectroscopies. Clearly distinct NMR peaks are observed for Sc in the eight-coordinated X site (pyrope and grs80) and in the six-coordinated Y site (grossular and grs80). X-ray and NMR data agree that only eight-coordinated Sc is present in pyrope and that six-coordinated Sc is predominant in grossular; however, the XRD results also indicated significant X and Z site (four-coordinated) Sc in the Ca-rich garnet. Possible reasons for this apparent discrepancy are discussed. We demonstrate that 45 Sc NMR is potentially a useful new method for studies of the site occupancies of Sc 3+ in oxides and silicates, at least in experimental systems where its concentration is a few percent or greater.

This paper reports a single-crystal unpolarized- light FTIR study in the OH-stretching region of a suite of well-characterized Ti-rich pargasites from Lherz (French Pyrenees). All amphiboles studied have fairly constant M-site composition, with Al-[6](tot) similar to 0.55 atoms per formula unit (apfia), Ti-[6] similar to 0.45 apfia, and Fe-[6](3+) similar to 0.40 apfu. SIMS and SREF data show all samples to have an 03 anion composition of OH approximate to O2- approximate to 1.0 apfu, with negligible F. The FTIR spectra show for all samples a broad absorption consisting of several overlapping bands; three main components can be recognized: similar to 3710, 3686, and 3660 cm(-1), respectively, with an asymmetric tail extending to lower frequency. Six Gaussian components can be fitted to the spectra; comparison with spectra of both synthetic and natural pargasites allows five of these components to be assigned to local configurations involving OH-O-2- at the 03 site, thus showing that coupling with an O2- anion through an A-cation significantly affects band position. Infrared spectroscopy can detect the presence of O2- in amphiboles in chemically favorable cases, i.e., in the absence of F. Moreover, the FTIR spectra show that all octahedral configurations involving Ti-M1(4+) or Fe-M1(3+) Fe-M3(3+) are associated with O2- at both adjacent 03 sites, and that Al-M3 is focally associated with OH, confirming SRO models based on structure refinement results.

Comprehensive knowledge of the order-disorder relations in amphiboles is essential to (1) complete understanding of the crystal chemistry of these minerals, and to (2) the use of amphiboles in thermodynamic calculations (e.g., of temperature and pressure of equilibration) where accurate activity models are critical to the accuracy of such treatments. Moreover, such information is essential to our understanding of phase relations, optical and electrical properties and dehydrogenation mechanisms. As a result, more effort has been expended on characterizing site occupancies in amphiboles than in any other group of minerals. Hawthorne (1983a,b) reviewed in detail all work prior to 1983. Here, we will briefly summarize this work, and focus more on what has been learned since then. We will briefly review the common methods of deriving site populations. It is important that everyone who uses site populations has an appreciation of the methods used to derive this information, as a significant fraction of the data in the literature is wrong, and the user has to be in a position to assess the accuracy and precision of the data that they will use. The most comprehensive method of deriving site populations is crystal-Structure REFinement (SREF), as this method senses every atom (in significant amounts) in a crystal. However, this universality has a negative side. Some atomic species cannot be distinguished as they scatter radiation in a very similar way. Different types of radiation (e.g., X-rays, neutrons) can compensate for this drawback: for example, X-ray scattering cannot easily distinguish between Fe and Mn or Fe and Ti (differences in size of these species can be used for this purpose, but this becomes inaccurate to ineffective in more complicated compositions), whereas neutron scattering can distinguish these species. However, there are many instances where such differentiation is not possible. It is here that …

This chapter provides an introduction to the crystal structure, crystal chemistry and chemical composition of the amphiboles. It is not an exhaustive treatment; it is intended as an introduction to the material discussed in the following chapters. More extensive discussion of many points is given in Hawthorne (1981, 1983a), although all later developments are discussed in some detail here. Published crystal-structure refinements are listed in Appendix I. The general chemical formula of the amphiboles can be written as \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[A\ B\_{2}\ C\_{5}\ T\_{8}\ O\_{22}\ W_{2}\] \end{document} where Minor elements such as Zn, Ni2+, Co2+, V3+, Sc, Cr3+ and Zr are also observed as C cations. In a mineral group as chemically complicated as the amphiboles, there are many problems connected with (1) the measurement of chemical composition, and (2) calculation of the chemical formula. ### Chemical composition The chemical composition of an amphibole is most commonly produced by electron microprobe analysis (EMPA). Instrumentation is very reliable and data reduction (including matrix corrections) are accurate. The main source of error is almost certainly errors in standards, a problem that can be dealt with in a simple but tedious fashion by cross-analyzing all standards. A more serious problem involves the components that cannot be analyzed (or analyzed accurately) by EMPA. Of particular relevance with regard to amphiboles are FeO vs. Fe2O3, Li2O and H2O, all of which occur commonly as highly variable constituents in amphiboles. We will focus on microbeam methods of …

The crystal-chemical formula and the major-element composition of amphiboles have been discussed in Hawthorne and Oberti (2007a), and the amphibole compositional space has been defined in terms of root-names and allowed charge arrangements in Hawthorne and Oberti (2007b). Although the number of possible homovalent substitutions occurring at the various structural sites is very high, geochemically exotic cations generally do not reach the limits required to assign a distinct prefix to the root-name. Thus prefixes are so far confined to the presence of Na, K, Mg, Al, Ti, Mn, Fe, F and Cl. In this chapter, we examine the new amphibole compositions which have been found and characterized since 1981, i.e. since the publication of volume 9A of the MSA Reviews in Mineralogy. We divide the chapter in two sections. The first section describes new charge arrangements found in Nature, and the second section describes the extensive studies of synthetic amphiboles of novel composition done to clarify the crystal chemistry of exotic cations which are normally found as minor components. This chapter deals exclusively with monoclinic amphiboles, as the compositional space of orthorhombic amphiboles has not expanded since the former review. Although natural occurrences of protoamphibole (with space group Pnmn ) have been described only in the last twenty years (Sueno et al. 1998; Konishi et al. 2003), their composition is within the compositional range previously defined for Pnma amphiboles. The main extensions of the traditional amphibole compositional space recognized in between the 1978 and the 1997 classification schemes (Leake 1978; Leake et al. 1997) are due to the discovery of: (1) sadanagaite, calcic amphiboles of ideal compositions AR+ BCa2 C(R2+3R3+2) T(Si5Al3) O22 W(OH)2 (Shimazaki et al. 1984; Sokolova et …