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The Mount Grace metamorphosed carbonatites (Late Devonian) outcrop as thin (0.5–4 m), laterally discontinuous, strata-bound mappable lenses within the Monashee complex of the southeastern Canadian Cordillera. The host stratigraphic sequence (Monashee cover gneiss) was metamorphosed and deformed in the Late Cretaceous to early Eocene followed immediately by exhumation of the Frenchman Cap and Thor Odin domes. We present seven stratigraphic logs for Mount Grace carbonatites including new and previously described outcroppings spanning ∼30 km. The Mount Grace carbonatite units were deposited regionally within or near the top of a shallow marine sedimentary sequence within miogeoclinal strata of the western margin of paleo-North America (Laurentia). The distribution of the Mount Grace carbonatite lithofacies and the preserved depositional structures and textures suggest that these are pyroclastic deposits resulting from phreatomagmatic eruptions. Our new data enhance the volcanological story with an eruption scenario involving phreatomagmatic reactions and deposition from pyroclastic density currents, sourced from multiple centers within a field of monogenetic maar volcanoes. The distribution of the Mount Grace carbonatites parallel to the western margin of the paleo-North American continent correlates well with regional Late Devonian alkaline magmatism associated with development of an extensional back-arc basin. [ABSTRACT FROM AUTHOR]

Cobalt-blue spinel from two localities (Qila and Trailside) on Baffin Island, Nunavut, Canada, are compared with other spinels from 12 occurrences in the same geological terrane and to Co-bearing blue spinel from other localities worldwide. Qila spinel is suitable for cutting cabochons, which commonly incorporate small amounts of associated calcite, dolomite, corundum, fluorapatite, pargasite and other silicates, as well as secondary cobaltpentlandite and fluid inclusions. Trailside spinel can be faceted into small gemstones (generally <0.2 ct), which rarely contain magnesite, fluorapatite, muscovite and CO2-rich fluid inclusions. The bright blue colour of the spinels from Qila and Trailside is due to TCo2+, although they also contain other chromophoric elements such as Fe and traces of Cr, Mn and V. Compared with other Mg-Al spinels from Baffin Island, those from Qila and Trailside are generally enriched in Co, Ni, Mn, Li and Be, and depleted in Ti, V and Cr. In addition, the Qila and Trailside Co-blue spinels are fairly chemically distinct from those of other world localities: they are depleted in V and Ti, fairly poor in Cr and Zn, and considerably enriched in Co and Mn. A new approach for the preliminary chemical discrimination of gem spinels is proposed by plotting the weighted chromophore concentrations in a ternary diagram (i.e. Cr+V vs 40×Co vs Fe/8). These weighted percentage values are also plotted against the ppmw concentrations of the chromophoric elements in X-Y plots, which provide further correlations of high Co with vivid Co-blue spinel and elevated Fe with overly dark non-gem spinel. This method can be applied to samples that are difficult or inefficient to characterise using spectroscopy, such as spinel grains in heavy-mineral concentrates obtained during regional exploration programmes. [ABSTRACT FROM AUTHOR]

The sparkle and luster of gemstones has made them prized objects for thousands of years. Gems are valued for their color, luster, transparency, durability and high value-to-volume ratio. Because many [...]

Joelbruggerite, ideally [Pb.sub.3][Zn.sub.3]([Sb.sup.5+], [Te.sup.6+])[As.sub.2][O.sub,13](OH,O), is a new arsenate mineral (IMA2008-034) and the [Sb.sup.5+] analog of dugganite, from the Black Pine mine, 14.5 km northwest of Philipsburg, Granite County, Montana. It is usually found perched on mimetite; other species that may be present include malachite, azurite, pseudomalachite, chalcocite, beudantite-corkite, duftite, dugganite, and kuksite, in milky quartz veins. Joelbruggerite occurs as barrel-shaped or prismatic crystals up to about 50 [micro]m across in various shades of purple. The crystals have an adamantine luster and a white streak. Mohs hardness is about 3. The fracture is irregular, and the tenacity is brittle. Joelbruggerite crystals are uniaxial (-), with a calculated refractive index of n = 1.993, and weakly pleochroic: X Y = gray, Z = purple; absorption: Z > X = Y. Crystals show straight extinction and are length-fast. The empirical chemical formula (mean of 5 electron microprobe analyses) calculated on the basis of 14 [O + OH] anions is [[Pb.sub.3.112]([Zn.sub.2.689][Fe.sup.2+.sub.0.185]).sub.[SIGMA]2.874] [([Sb.sup.5+.sub.0.650][Te.sup.6+.sub.0.451].sub.[SIGMA]1.101] [([As.sub.1.551][P.sub.0.203][Si.sub.0.160].sub.[SIGMA]1.914] [O.sub.13.335[(OH).sub.0.665]. Joelbruggerite is trigonal, space group P321, a = 8.4803(17),c 5.2334(12) [Angstrom], V= 325.94(12) [[Angstrom].sup.3], Z = 1. The five strongest lines in the powder X-ray diffraction pattern are [[d.sub.obs] in [Angstrom] (I) (hk/)]: 3.298 (100) ( 111 ), 3.008 (89) (021), 1.905 (39) (122, 131), 2.456 (36) (012, 121,030), and 1.609 (30) (112, 132, 231, 140). The crystal structure was solved from single-crystal X-ray diffraction data and refined to [R.sub.1] = 0.038 on the basis of 604 unique reflections with F > 4[sigma](F). It is composed of heteropolyhedral sheets of edge-sharing (Sb,Te)[O.sub.6] octahedra and Pb[O.sub.8] disphenoids, oriented parallel to (001). The sheets are cross-linked by As[O.sub.4] and Zn[O.sub.4] tetrahedra, which share comers to form an interlinked, two- and three- connected two-dimensional net parallel to (001). The mineral is named for JoEl Brugger (born 1967), Swiss-Australian mineralogist, for his contributions to mineralogy. Keywords: Joelbruggerite, new mineral, [Sb.sup.5+], arsenate, Black Pine mine, dugganite, crystal structure, bond valence

The famous amethyst geodes of Brazil and Uruguay rarely contain crystals of 'skunk' calcite, wherein microcrystals of goethite form sharp, narrow black bands on rhombohedral calcite faces. Close study reveals [...]

We report on temperature dependencies of infrared (IR) fundamental, combination, and overtone vibrations of hydroxyl species (OH) in nominally anhydrous minerals (e.g., titanite), ferroelectric crystals (K[Ta.sub.1] [sub.x][Nb.sub.x][O.sub.3], KTN), layer silicates (talc, mica, and pyrophyllite), and hydrous minerals such as apatite and synthetic hydrous/deuterated garnets [[Ca.sub.3][A1.sub.2][([O.sub.4][H.sub.4]).sub.3] and [Ca.sub.3][Al.sub.2][([O.sub.4][D.sub.4]).sub.3]] for the temperature range of 20-300 K. Data obtained by high- resolution FTIR spectroscopy show that increasing temperature generally leads to a decrease in the band height and band area of fundamental vibrations of hydroxyl species, whereas the combination and first-overtone bands commonly show different temperature dependencies. The results show that in the investigated temperature range, the variations of the band height and area for different OH bands (especially for combinations and overtones) on cooling or heating do not reflect changes in OH concentrations in the materials, but relate to temperature-dependent absorption coefficients. The observations imply that absorption coefficients calibrated at room temperature cannot necessarily be used for the determination of hydroxyl contents at other temperatures. Keywords: Infrared spectroscopy, low temperature, apatite, hydrous garnet, pyrophyllite, tale, sericite, titanite

The electron microprobe compositions and crystal structure of seven members of the grandidierite-ominelite (Mg[Al.sub.3]BSi[O.sub.9-[Fe.sup.2+][Al.sub.3]BSi[O.sub.9]) series with X = ([Fe.sup.2+] + Mn + Zn)/([Fe.sup.2+] + Mn + Zn + Mg) ranging from 0.00 to 0.52 were studied to determine the geometric effects of Fe substitution for Mg on the crystal structures. Calculating [Fe.sup.3+] from the electron microprobe analyses gave 0.04-0.06 [Fe.sup.3+] apfu, but such small amounts at the Al sites could not be detected in the refinements. Regression equations derived from single-crystal X-ray diffraction data show that b increases by 0.18 [Angstrom] from X=0-1. The crystal structure refinements show that the most significant changes involve the (Mg,[Fe.sup.2+])[O.sub.5] polyhedron, which increases in volume by 0.36 [[Angstrom].sup.3] (5.0%), largely as a result of expansion of the MgFe05, -O2, and -O6 (x2) bond distances, which increase by 0.09 (4.4%), 0.06, and 0.04 [Angstrom], respectively. Other significant changes include increasing Ol-MgFe-O2 (3.44[degrees]) and -A13-O5a angles (1.9[degrees]) and a decreasing O6-MgFe-O6b (-2.20[degrees]) angle. Significant increases ate also seen in the lengths of the O1-O2 (0.13 [Angstrom]) and O6-O5a (x2) (0.09 [Angstrom]) edges. The Si[O.sub.4] tetrahedra appear to respond to changes in the surrounding polyhedra by changing O-Si-O angles such that the tetrahedral angle variance and mean tetrahedral quadratic elongation increase with X. The B[O.sub.3] triangles appear to behave as relatively invariant units in the crystal structure. Regression equations obtained from the MgFe-O bond distances were used to determine a radius for [sup.v][Fe.sup.2+] of 0.70 [Angstrom]. Although our samples show little Mn, the presence of [Mn.sup.2+] at the MgFe site would be expected to cause more distortion than an equivalent amount of [Fe.sup.2+]. Substitution of Zn likely would have little effect. The presence of [Cr.sup.3+] at any of the Al sites would be expected to increase the size of the coordination sphere, but the substitution of [p.sup.5+] for Si at the Si sites would most likely decrease the Si-O bond distances. Keywords: Grandidierite, ominelite, crystal structure, substitution, borosilicates

SUMMARY This paper reviews the geology, mineralogy, and origin of the gem varieties of beryl, including emerald (green) and aquamarine (blue); it focuses on western Canada, especially the Yukon Territory, [...]

The influence of F substitution on the local structure of Al in the tetrahedral and octahedral sheets of synthetic Al-rich phlogopite samples with nominal gel compositions of K([Mg.sub.3-x][Al.sub.x] [[Al.sub.1+x][Si.sub.3-x][O.sub.10]] [(OH).sub.y][(F).sub.2-y] between 0.0 [less than or equal to] x [less than or equal to] 0.8 and 0.5 [less than or equal to] y [less than or equal to] 1.8, was studied by [sup.27]Al MAS, MQMAS, {[sup.1]H/[sup.19]F} [vector] [sup.27]Al 2D CPMAS (HETCOR) and {[sup.1]H/[sup.19]F} [sup.27]Al REDOR solid-state NMR an by IR spectroscopy. Changes in intensity of the absorption bands in the OH-stretching region of the IR spectra clearly indicate the incorporation of octahedral Al. Signais from the different phases can be separated in the [sup.27]Al MQMAS NMR spectra by generation of an isotropic dimension in F1. The [sup.27]Al quadrupolar parameters of the four phases were estimated from [sup.27]Al MAS NMR spectra obtained at 104.26 and 208.42 MHz. The quadrupolar coupling constant and isotropic chemical shift increases with increasing Al content for the [sup.IV]Al site in phlogopite. The [sup.VI]Al site shows a clear increase of the asymmetry parameter and [C.sub.Q] with increasing F content. The estimated [sup.27]Al signal areas show the lowest amount of impurity phases at high OH contents and a stabilization of [sup.VI]Al sites by hydroxyl groups. The {[sup.1]H} [vector] [sup.27]Al 2D CPMAS (HETCOR) NMR experiment at short contact rimes provides information about site neighborhoods of tetrahedral Al sites and [Mg.sub.3]OH as well as [Mg.sub.2]AlOH sites, whereas magnetization is only transferred to the octahedral Al sites from hydroxyl groups in [Mg.sub.2]AlOH sites. The {[sup.1]H/[sup.19]F} [vector] [sup.27]Al 2D CPMAS (HETCOR) NMR spectrum is dominated by [sup.IV]Al sites coupled to the [Mg.sub.3]F complex in phlogopite. Resonances from [Mg.sub.2]AlF complexes are not observed. Finally, the {[sup.1]H/[sup.19]F} [sup.27]Al REDOR experiments support the results of the 2D CPMAS (HETCOR) experiments.

Celleriite, □ ( Mn 2 2 + Al) Al 6 ( Si 6 O 18 ) ( BO 3) 3 (OH) 3 (OH) , $\square \,\left(\text{Mn}_{2}^{2+}\text{Al} \right)\text{A}{{\text{l}}_{6}}\left(\text{S}{{\text{i}}_{6}}{{\text{O}}_{18}} \right){{\left(\text{B}{{\text{O}}_{3}} \right)}_{3}}{{(\text{OH})}_{3}}(\text{OH}),$ is a new mineral of the tourmaline supergroup. It was discovered in the Rosina pegmatite, San Piero in Campo, Elba Island, Italy (holotype specimen), and in the Pikárec pegmatite, western Moravia, Czech Republic (co-type specimen). Celleriite in hand specimen is violet to gray-blue (holotype) and dark brownish-green (co-type) with a vitreous luster, conchoidal fracture, and white streak. Celleriite has a Mohs hardness of ~7 and a calculated density of 3.13 and 3.14 g/cm3 for holotype and its co-type, respectively. In plane-polarized light in thin section, celleriite is pleochroic (O = pale violet and E = light gray-blue in holotype; O = pale green and E = colorless in co-type) and uniaxial negative. Celleriite has trigonal symmetry: space group R3m, Z = 3, a = 15.9518(4) and 15.9332(3) Å, c = 7.1579(2) and 7.13086(15) Å, V = 1577.38(9) and 1567.76(6) Å3 for holotype and co-type, respectively (data from single-crystal X‑ray diffraction). The crystal structure of the holotype specimen was refined to R1 = 2.89% using 1696 unique reflections collected with MoKα X‑ray intensity data. Structural, chemical, and spectroscopic analyses resulted in the formulas: x (□ 0.58 Na 0.42 ) ∑ 1.00 Y ( Mn 1.39 2 + Fe 0.16 2 + Mg 0.01 Al 1.14 Fe 0.01 3.0 Li 0.28 T 0.01 ) Σ 3.00 Z Al 6 [ T ( Si 5.99 Al 0.01 ) Σ 6.00 O 18 ] ( BO 3) 3 (OH) 3 w [ (OH) 0.65 F 0.03 O 0.32 ] Σ 1.00 (for holotype) $\begin{align}& \,\,\,\,{{\,}^{\text{x}}}{{\left({{\square }_{0.58}}\text{N}{{\text{a}}_{0.42}} \right)}_{\sum 1.00}}\text{Y}{{\left(\text{Mn}_{1.39}^{2+}\text{Fe}_{0.16}^{2+}\text{M}{{\text{g}}_{0.01}}\text{A}{{\text{l}}_{1.14}}\text{Fe}_{0.01}^{3.0}\text{L}{{\text{i}}_{0.28}}~{{\text{T}}_{0.01}} \right)}_{\Sigma 3.00}}^{\text{Z}}\text{A}{{\text{l}}_{6}}\left[ {{~}^{\text{T}}}{{\left(\text{S}{{\text{i}}_{5.99}}\text{A}{{\text{l}}_{0.01}} \right)}_{\Sigma 6.00}}{{\text{O}}_{18}} \right]{{\left(\text{B}{{\text{O}}_{3}} \right)}_{3}}{{(\text{OH})}_{3}} \\ & ^{\text{w}}{{\left[ {{(\text{OH})}_{0.65}}~{{\text{F}}_{0.03}}{{\text{O}}_{0.32}} \right]}_{\Sigma 1.00}}\,\text{(for}\,\text{holotype)} \\ \end{align}$ and X (□ 0.51 Na 0.49 ) Σ 1.00 Y ( Mn 0.90 2 + Fe 050 2 + Al 1.36 Fe 004 3 + Li 0.17 Zn 0.04 ) Σ 3.00 Z Al 6 [ T ( Si 5.75 B 0.25 ) Σ 6.00 O 18 ] ( BO 3) 3 (OH) 3 w [ (OH) 0.35 F 0.17 O 0.48 ] ∑ 1.00 (for co-type) $\begin{align}& \,\,\,\,\,{{\,}^{\text{X}}}{{\left({{\square }_{0.51}}\text{N}{{\text{a}}_{0.49}} \right)}_{\Sigma 1.00}}^{\text{Y}}{{\left(\text{Mn}_{0.90}^{2+}\text{Fe}_{050}^{2+}\text{A}{{\text{l}}_{1.36}}\text{Fe}_{004}^{3+}\text{L}{{\text{i}}_{0.17}}\text{Z}{{\text{n}}_{0.04}} \right)}_{\Sigma 3.00}}^{\text{Z}}\text{A}{{\text{l}}_{6}}\left[ ^{\text{T}}{{\left(\text{S}{{\text{i}}_{5.75}}~{{\text{B}}_{0.25}} \right)}_{\Sigma 6.00}}{{\text{O}}_{18}} \right]{{\left(\text{B}{{\text{O}}_{3}} \right)}_{3}}{{(\text{OH})}_{3}} \\ & ^{\text{w}}{{\left[ {{(\text{OH})}_{0.35}}~{{\text{F}}_{0.17}}{{\text{O}}_{0.48}} \right]}_{\sum 1.00}}\text{(for}\,\text{co-type)} \\ \end{align}$ Celleriite is a hydroxy species belonging to the X-site vacant group of the tourmaline supergroup. The new mineral was approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association, proposal no. 2019-089. In the Rosina pegmatite, celleriite formed an overgrowth at the analogous pole of elbaite–fluorelbaite–rossmanite crystals during the latest stage of evolution of pegmatite cavities after an event of a pocket rupture. In the Pikárec pegmatite, celleriite occurs as an intermediate growth sector of elbaite, princivalleite, and fluor-elbaite. [ABSTRACT FROM AUTHOR]

Interpretation of various exploration data, in particular geochemical prospecting, offers a powerful and rapid assessment of grass‐root projects in a green‐field terrain. Here, we present an example of the Collins epithermal prospect in Aceh Province, Indonesia. In this area, the Au+ base‐metal‐bearing sheeted quartz veins (individually mostly 2–4 cm wide), which are controlled by a 250 m wide by 800 m long NNE‐trending structural corridor within Paleogene sandstone and volcanic rocks, are the product of two main stages of deposition. Stage I formed veins with a sliver of cryptocrystalline quartz wall zone followed by an inner zone of comb quartz with interstitial rhombic adularia that terminates in open space. Stage I or main‐stage sulfide mineralization consisting of early galena + sphalerite and later chalcopyrite occurs with the quartz + adularia. Small amounts of galena also occur in the wall zone. Stage II mineralization brecciated Stage I veins and overprinted them with silicification characterized by vuggy texture. Mineralization associated with this episode consists of earlier chalcopyrite + sphalerite + tennantite–tetrahedrite and later, vug‐filling Au–Ag alloy (Ag0.37–0.41Au0.62–0.59). The above mineralized veins are successively flanked by silicic selvages, an illite + chlorite + pyrite ± kaolinite zone and a chlorite + epidote + carbonate + pyrite zone. Local supergene alteration induced replacement of galena by plumbogummite and anglesite and chalcopyrite by covellite. Data from fluid inclusion microthermometry in quartz indicated that the inner zone of Stage I veins formed from fluids with a 2.3 wt% salinity (0.5–3.3 wt% NaCl equivalent), at 174°C (155–211°C). Combining these physico‐chemical parameters with the mineral assemblage, the mineralization occurred under a reduced environment. Rock and soil assays indicate that elevated Au concentrations (up to 16.5 ppm over 1 m) occur along northeast‐trending zones and show a strong correlation with Pb, while Cu (up to 2.58% over 1 m), Zn, As, Sb, and Mo anomalies lie mostly at the periphery. The high‐grade mineralized veins correlate with moderate to high resistivity and chargeability zones, and the pseudosections of such geophysical signals are interpreted as reflecting coalesced or enlarged veins at depth, or inclined veins in other localities. The intermediate sulfidation affinity for Collins points to potential mineralization at depth as well as preservation of Au‐rich and sulfide‐poor zones in the less eroded areas. [ABSTRACT FROM AUTHOR]

The Silvana mine has produced an array of very fine to spectacular micromineral and thumbnail specimens including rare, fiery-orange pyrostilpnite, lustrous cubanite, pyrargyrite and stephanite as well as showy, irridescent [...]

The Engineer mine is a Dana locality for classic, botryoidal 'allemontite' (stibarsen and native arsenic). Several other minerals of interest to the collector are also found, including crystallized auriferous silver [...]

Magnesio-lucchesiite, ideally CaMg3Al6 (Si6O18)(BO3)3(OH)3O, is a new mineral species of the tourmaline supergroup. The holotype material was discovered within a lamprophyre dike that crosscuts tourmaline-rich metapelites within the exocontact of the O'Grady Batholith, Northwest Territories (Canada). Two additional samples were found at San Piero in Campo, Elba Island, Tuscany (Italy) in hydrothermal veins embedded in meta-serpentinites within the contact aureole of the Monte Capanne intrusion. The studied crystals of magnesio-lucchesiite are black in a hand sample with vitreous luster, conchoidal fracture, an estimated hardness of 7-8, and a calculated density of 3.168 (Canada) and 3.175 g/cm³ (Italy). In plane-polarized light, magnesio-lucchesiite is pleochroic (O = dark brown, E = colorless) and uniaxial (-); its refractive index values are nω = 1.668(3) and nε = 1.644(3) (Canada), and nω = 1.665(5) and nε = 1.645(5) (Italy). Magnesio-lucchesiite is trigonal, space group R3m, Z = 3, with a = 15.9910(3) Å, c = 7.2224(2) Å, V = 1599.42(7) ų (Canada) and with a = 15.9270(10) Å, c = 7.1270(5) Å, V = 1565.7(2) ų (Italy, sample 1). The crystal structure of magnesio-lucchesiite was refined to R1 = 3.06% using 2953 reflections with Fo > 4σ(Fo) (Canadian sample; 1.96% / 1225 for the Italian sample) The Canadian (holotype) sample has the ordered empirical formula X(Ca0.60Na0.39K0.01) ∑1.00Y(Mg2.02 Fe2+0.62 Fe3+0.09Ti0.25 V0.01Cr0.01)∑3.00 Z(Al5.31Fe3+0.69)∑6.00 T(Si5.98Al0.02)∑6.00O18 (BO3)3V(OH)2.59 O0.41∑3.00 W(O0.78F0.22)∑1.00. The Italian (co-type) material shows a wider chemical variability, with two different samples from the same locality having ordered chemical formulas: X(Ca0.88Na0.12)∑1.00 Y(Mg1.45Fe2+0.40 Al0.79Fe3+0.36)∑3.00 ZAl6T(Si5.05Al0.95) ∑6.00O18(BO3)3 V(OH)2.90O0.10∑3.00 W(O0.98F0.02)∑1.00 (sample 1) and X(Ca0.71Na0.21□0.08) ∑1.00Y(Mg2.49 Fe2+0.41Ti0.10)∑3.00 Z(Al5.44Fe3+0.46 Mg0.09V0.01)∑6.00 T(Si5.87Al0.13)∑6.00 O18(BO3)3V(OH)3 WO0.61(OH)0.39∑1.00 (sample 2). Magnesio-lucchesiite is an oxy-species belonging to the calcic group of the tourmaline supergroup. It is related to lucchesiite by the homovalent substitution YFe ↔ YMg, and to feruvite by the homovalent and heterovalent substitutions YFe ↔ YMg and ZAl3+ + WO2- ↔ ZMg2+ + W(OH)1-. The new mineral was approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA 2019-025). Occurrences of magnesio-lucchesiite show that its presence is not restricted to replacement of mafic minerals only; it may also form in metacarbonate rocks by fluctuations of F and Al during crystallization of common uvitic tourmaline. High miscibility with other tourmaline end-members indicates the large petrogenetic potential of magnesio-lucchesiite in Mg,Al-rich calc-silicate rocks, as well as contact-metamorphic and metasomatic rocks. [ABSTRACT FROM AUTHOR]

Origin determination is of increasing importance in the gem trade. It is possible because there is a close relationship between the geological environment of formation and the physical and chemical properties of gemstones, such as trace element and isotopic compositions, that can be measured in the laboratory using combinations of increasingly sophisticated instrumentation. Origin conclusions for ruby, sapphire, and emerald make up the bulk of demand for these services, with growing demand for alexandrite, tourmaline, and spinel. However, establishing origin with a high degree of confidence using the capabilities available today is met with varying degrees of success. Geographic origin can be determined with a high level of confidence for materials such as emerald, Paraíba-type tourmaline, alexandrite, and many rubies. For some materials, especially blue sapphire and some rubies, the situation is more difficult. The main problem is that if the geology of two deposits is similar, then the properties of the gemstones they produce will also be similar, to the point where concluding an origin becomes seemingly impossible in some cases. Origin determination currently relies on a combination of traditional gemological observations and advanced analytical instrumentation. [ABSTRACT FROM AUTHOR]

The great challenge of geographic origin determination is to connect the properties and features of individual gems to the geology of their deposits. Similar geologic environments can produce gems with similar gemological properties, making it difficult to find unique identifiers. Over the last two decades, our knowledge of corundum and emerald deposit formation has improved significantly. The mineral deposits are classically separated into primary and secondary deposits. Primary corundum deposits are subdivided into two types based on their geological environment of formation: (1) magmatic and (2) metamorphic. Magmatic deposits include gem corundum in alkali basalts as in eastern Australia, and sapphire in lamprophyre and syenite as in Montana (United States) and Garba Tula (Kenya), respectively. Metamorphic deposits are divided into two subtypes (1) metamorphic deposits sensu stricto (in marble; mafic and ultramafic rocks, or M-UMR), and (2) metamorphicmetasomatic deposits characterized by high fluid-rock interaction and metasomatism (i.e., plumasite or desilicated pegmatites in M-UMR and marble, skarn deposits, and shear zone-related deposits in different substrata, mainly corundum-bearing Mg-Cr-biotite schist). Examples of the first subtype include the ruby deposits in marble from the Mogok Stone Tract or those in M-UMR from Montepuez (Mozambique) and Aappaluttoq (Greenland). The second subtype concerns the sapphire from Kashmir hosted by plumasites in M-UMR. Secondary corundum deposits (i.e., present-day placers) result from the erosion of primary corundum deposits. Here, corundum is found in the following types of deposits: eluvial (derived by in situ weathering or weathering plus gravitational movement), diluvial (scree or talus), colluvial (deposited at the base of slopes by rainwash, sheetwash, slow continuous downslope creep, or a combination of these processes), and alluvial (deposited by rivers). Today, most sapphires are produced from gem placers related to alkali basalts, as in eastern Australia or southern Vietnam, while placers in metamorphic environments, such as in Sri Lanka (Ratnapura, Elahera) and Madagascar (Ilakaka), produce the highest-quality sapphires. The colluvial Montepuez deposit in Mozam bique provides a huge and stable supply of clean and very highquality rubies. Primary emerald deposits are subdivided into two types based on their geological environment of formation: (1) tectonic-magmatic-related (Type I) and (2) tectonic-metamorphic-related (Type II). Several subtypes are defined and especially Type IA, hosted in MUMR, which accounts for about 70% of worldwide production (Brazil, Zambia, Russia, and others). It is characterized by the intrusion of pegmatites or quartz veins in M-UMR accompanied by huge hydrothermal fluid circulation and metasomatism with the formation of emerald-bearing desilicated pegmatite (plumasite) and biotite schist. Type IB in sedimentary rocks (China, Canada, Norway, Kazakhstan, and Australia) and Type IC in granitic rocks (Nigeria) are of minor importance. The subtype Type IIA of metamorphic deposits is related to hydrothermal fluid circulation at high temperature, in thrust fault and/or shear zones within M-UMR of volcano-sedimentary series, such as at the Santa Terezinha de Goiás deposit in Brazil. The subtype Type IIB is showcased by the Colombian emerald deposits located in the Lower Cretaceous black shales of the Eastern Cordillera Basin. These are related to the circulation of hydrothermal basinal fluids in black shales, at 300-330°C, that dissolved evaporites in (1) thrust and tear faults for the deposits of the western emerald zone (Yacopi, Coscuez, Muzo, Peñas Blancas, Cunas, and La Pita mines) and (2) a regional evaporite level intercalated in the black shales or the deposits of the eastern emerald zone (Gachalá, Chivor, and Macanal mining districts). Secondary emerald deposits are unknown because emerald is too fragile to survive erosion and transport in rivers. [ABSTRACT FROM AUTHOR]

Canada exhibits many of the challenges involved with exploring for coloured stones in countries with very low population densities, temperate-to-arctic climates and a lack of infrastructure hindering access to most prospective areas. Despite this, a number of discoveries have occurred, mainly during the past two decades. These include emeralds from Northwest Territories (1997) and Yukon (1998); sapphire (2002) and spinel (from 1982)—including cobalt-blue stones—from Baffin Island in Nunavut; and ruby and pink sapphire (2002) from British Columbia. Such discoveries can be assisted by undertaking scientific research into gem formation, as well as by applying exploration criteria developed elsewhere to uncharted territory. Future exploration in Canada and other countries facing similar challenges will likely benefit from additional geological studies to identify prospective areas and features; innovative means of transportation, such as boats instead of aircraft; drones for exploring rugged terrain; hyperspectral imaging for mineral sensing; surveying with UV lamps to identify minerals associated with gem mineralisation; and careful prospecting (including field mapping and collecting heavy mineral concentrates) by experienced individuals. [ABSTRACT FROM AUTHOR]

Sakhaite, ca. Ca48Mg16(BO3)32(CO3)16(HCl,H2O)2, is a rare rock-forming borate-carbonate mineral typically occurring in high-temperature, low-pressure calcareous skarns. It forms a complete solid solution with harkerite, ca. Ca48Mg16[AlSi4(O,OH)16]4(BO3)16(CO3)16(HCl,H2O)2. The solid solution can be described with the general formula Ca 48 (Mg , Fe , Mn) 16 (CO 3) 16 [ Al a Si 5 − a (O , OH) 16 ] y (BO 3) 32 − 4 y (HCl , H 2 O) n $$\begin{array} {} {\rm{C}}{{\rm{a}}_{48}}{({\rm{Mg}},{\rm{Fe}},{\rm{Mn}})_{16}}{({\rm{C}}{{\rm{O}}_3})_{16}}{[{\rm{A}}{{\rm{l}}_a}{\rm{S}}{{\rm{i}}_{5 - a}}{({\rm{O}},{\rm{OH}})_{16}}]_y}{({\rm{B}}{{\rm{O}}_{\rm{3}}})_{32 - 4y}}{({\rm{HCl}},{{\rm{H}}_2}{\rm{O}})_n}\end{array} $$ where ymax = 8 and nmax = 16 – y. In this study, we examine samples of sakhaite and harkerite from four localities worldwide: Titovskoye deposit, Sakha Republic, Russia (type locality for sakhaite); Solongo B deposit, Buryatia Republic, Russia; Camas Malag, Skye, Scotland (type locality for harkerite); as well as a sakhaite-like mineral from the Kombat Mine, Tsumeb. The Si:B ratios of the samples ranged from that of end-member sakhaite (containing B only) to that of end-member harkerite (Si:B = 1:1), with several intermediate compositions. All samples were deficient in B relative to the ideal composition, implying significant substitution for borate groups. The Si:Al ratio of silicate-containing samples ranged from the ideal 4:1 to 4:1.5, implying substitution of Al at the Si site. The cubic unit-cell parameter was found to increase linearly with increasing Si content, except for the sakhaite-like mineral from Tsumeb. This mineral was found to have significant substitution of Pb for Ca (0.4–0.5 apfu) and was poor in Cl, which in most sakhaite and harkerite samples occupies the interstitial site surrounded by four borate groups. This interstitial site in the Tsumeb samples appears to be, instead, mainly occupied by H2O, which may qualify the mineral as a distinct species. [ABSTRACT FROM AUTHOR]

Natural samples of the rare earth element (REE)-bearing silicate minerals cerite, mosandrite, kainosite, zircon, and eudialyte were studied using reflectance spectroscopy in the visible to short-wave infrared regions (500 to 2500 nm) and further characterized by scanning electron microscopy and electron microprobe analysis. Spectral features of these minerals are driven primarily by 4f-4f intraconfigurational electronic transitions of trivalent lanthanides, as well as 5f-5f electronic transitions of uranium and vibrational overtones and combinations of H2O and OH–. Spectra of eudialyte are also impacted by relative amounts of IVFe2+ and VFe2+. Respective spectra of these REE-bearing silicate minerals are sufficiently distinct to enable spectral classification. Spectral variability (e.g., band depths and locations) of some specific REE-related absorptions, such as an Er3+- and Yb3+-related absorption near 978 nm and Nd3+-related absorptions near 746, 803, and 875 nm, are interpreted to be driven by cation site differences in the crystal structures. This work adds to the growing understanding of REE-bearing mineral reflectance spectroscopy, which facilitates detection, identification, and quantification of REE-bearing silicate minerals in remote sensing applications. This is especially relevant for hyperspectral imaging spectroscopy with high spatial resolutions where the spectral response of a pixel becomes increasingly dominated by mineralogy rather than lithology. [ABSTRACT FROM AUTHOR]

Calc-alkaline lamprophyre dikes are hosted by tourmalinized metasedimentary rocks in the Northwest Territories, Canada. Some of these lamprophyre dikes are cross-cut by aplite and pegmatite dikes, as well as tourmaline-bearing quartz veins that were all derived from the nearby granitic O'Grady Batholith. The lamprophyre dikes are composed of actinolite to magnesio-hornblende, plagioclase, K-feldspar and quartz with minor phlogopite (up to 4.13 wt. % TiO2), titanite, apatite, pyrite, allanite-(Ce), and zircon. A zone near the margin of one of the dikes has been altered to tourmaline associated with actinolite to magnesio-hornblende, clinochlore, titanite and quartz, with minor clinopyroxene and apatite. Two generations of tourmaline are recognized: Tur I occurs in quartz at the margin of the dike and Tur II forms a massive aggregate with common inclusions of other minerals in an altered lamprophyre zone near the margin of the dike. The vast majority of the analyzed tourmaline is Al-deficient, with less than 6 apfu Al at the Z site (on average 5.691 apfu in Tur I and 5.601 apfu in Tur II). Tur I is mostly dravite with uvite, plus minor feruvite and fluor-uvite, while Tur II contains a greater proportion uvite, feruvite, and fluor-uvite. The most evolved tourmaline compositions observed are feruvite with up to 2.17 wt. % TiO2, and fluor-uvite with up to 0.84 wt. % F. The tourmaline composition reflects the unique geochemical environment in which it crystallized; from Tur I to Tur II, tourmaline becomes richer in Ca-, Fe-, and Ti, presumably due to the reaction of B-bearing fluids with the Al-poor, Ca-, Mg-Fe-, and Ti-bearing minerals in the lamprophyre dike. The high F contents of some tourmaline species suggest that it crystallized from fluids derived from the aplite and pegmatite dikes. [ABSTRACT FROM AUTHOR]

Phosphorus is the central ingredient in fertilizer that allows modern agriculture to feed the world's population. This element, also critical in a host of industrial applications, is a nonrenewable resource that is sourced primarily from the phosphatic mineral apatite, hosted in sedimentary and igneous ores. World phosphate resources are estimated by the U.S. Geological Survey at ca. 300,000 Mt, of which 95% are sedimentary and 5% are igneous. Current known USGS reserve estimates are sufficient for a maximum of 200 to 300 years; the exploration and discovery of new resources, enhanced mining technologies, and new technologies aimed at the recovery and recycling of P from sewage and agricultural runoff will all contribute to extending P production. Igneous ores are generally associated with Phanerozoic carbonatites and silica-deficient alkalic intrusions that typically average 5 to 15 wt % P2O5, which can be beneficiated to high-grade concentrates of at least 30 wt % P2O5 with few contaminants. Carbonatites are typically the smallest and youngest parts of a carbonatite-alkaline rock complex that formed during fractional crystallization of a calcic parental alkaline silicate melt, or from liquid immiscibility of a carbonate-rich nephelinite that underwent magmatic fractionation and differentiation during ascent from the mantle source. Fluorapatite generally crystallizes early, near the liquidus, and over a small temperature interval below the apatite saturation temperature that varies strongly with temperature, SiCL and CaO concentrations, and the aluminosity of the melt. Carbonatite-alkaline rock complexes commonly possess a concentric, zonal structure thought to reflect caldera volcanism. Pathfinder elements in soils, sediments, tills, and vegetation include Nb, rare earth elements (REEs), P, Ba, Sr, F, U, and Th, and in water, F, Th, and U are indicators. Remote sensing techniques with the ability to identify minerals rich in CO3, REEs, and Fe2+ that are characteristic of carbonatites are also important exploration tools that may provide vectors to ore. Sedimentary phosphorite is a marine bioelemental sedimentary rock that contains >18 wt % P2O5. While small peritidal phosphorites formed in Precambrian coastal environments, economically significant upwelling- related phosphorite did not accumulate until the late Neoproterozoic and continued through the Phanerozoic. Coastal upwelling delivered deep, P-rich waters to continental shelves and in epeiric seas to drive phospho-genesis and form the largest phosphorites on Earth. High-grade deposits formed as a result of hydraulic concentration of phosphate grains to form granular beds with minimal gangue. The amalgamation of these beds into decameter-thick, stratiform ore zones is generally focused along the maximum flooding surface, which is a primary exploration target in upwelling-related phosphorite. In addition to P, other elements concentrated in igneous and sedimentary phosphorites are Se, Mo, Zn, Cu, and Cr, which are important agricultural micronutrients. Other saleable by-products include U and REEs. The U concentration in sedimentary phosphorite is generally between 50 and 200 ppm, but can be as high as 3,000 ppm, making it an increasingly important source of U for the nuclear industry. The concentration of REEs in some sedimentary phosphorites is comparable to the world's richest igneous and Chinese clay-type REE deposits. The source of the dissolved P in upwelling ocean water is ultimately derived from the chemical weathering of continental rocks, the process that links igneous and sedimentary phosphorites through time and space. The covarying temporal relationship of igneous and sedimentary deposits suggests that plate tectonics and the concentration of apatite in a progressively more felsic crust underpins the feedback processes regulating the biogeochemical cycling of P Critical to the generation of greenfield exploration targets is the recognition that large P deposits emerged in the late Neoproterozoic. The geological environments conducive for exploration can be constrained from an understanding of ore-forming processes by the use of complementary petrological techniques, including fieldwork, petrography, sedimentology, sequence stratigraphy, and geochemistry. [ABSTRACT FROM AUTHOR]

Radiation damage in minerals is caused by the α-decay of incorporated radionuclides, such as U and Th and their decay products. The effect of thermal annealing (400-1000 K) on radiation-damaged pyrochlores has been investigated by Raman scattering, X-ray powder diffraction (XRD), and combined differential scanning calorimetry/thermogravimetry (DSC/TG). The analysis of three natural radiation-damaged pyrochlore samples from Miass/Russia [6.4 wt% Th, 23.1·1018 α-decay events per gram (dpg)], Panda Hill/Tanzania (1.6 wt% Th, 1.6·1018 dpg), and Blue River/Canada (10.5 wt% U, 115.4·1018 dpg), are compared with a crystalline reference pyrochlore from Schelingen (Germany). The type of structural recovery depends on the initial degree of radiation damage (Panda Hill 28%, Blue River 85% and Miass 100% according to XRD), as the recrystallization temperature increases with increasing degree of amorphization. Raman spectra indicate reordering on the local scale during annealing-induced recrystallization. As Raman modes around 800 cm−1 are sensitive to radiation damage (M. T. Vandenborre, E. Husson, Comparison of the force field in various pyrochlore families. I. The A2B2O7 oxides. J. Solid State Chem. 1983, 50, 362, S. Moll, G. Sattonnay, L. Thomé, J. Jagielski, C. Decorse, P. Simon, I. Monnet, W. J. Weber, Irradiation damage in Gd2Ti2O7 single crystals: Ballistic versus ionization processes. Phys. Rev. 2011, 84, 64115.), the degree of local order was deduced from the ratio of the integrated intensities of the sum of the Raman bands between 605 and 680 cm−1 divided by the sum of the integrated intensities of the bands between 810 and 860 cm−1. The most radiation damaged pyrochlore (Miass) shows an abrupt recovery of both, its short- (Raman) and long-range order (X-ray) between 800 and 850 K, while the weakly damaged pyrochlore (Panda Hill) begins to recover at considerably lower temperatures (near 500 K), extending over a temperature range of ca. 300 K, up to 800 K (Raman). The pyrochlore from Blue River shows in its initial state an amorphous X-ray diffraction pattern superimposed by weak Bragg-maxima that indicates the existence of ordered regions in a damaged matrix. In contrast to the other studied pyrochlores, Raman spectra of the Blue River sample show the appearance of local modes above 560 K between 700 and 800 cm−1 resulting from its high content of U and Ta impurities. DSC measurements confirmed the observed structural recovery upon annealing. While the annealing-induced ordering of Panda Hill begins at a lower temperature (ca. 500 K) the recovery of the highly-damaged pyrochlore from Miass occurs at 800 K. The Blue-River pyrochlore shows a multi-step recovery which is similarly seen by XRD. Thermogravimetry showed a continuous mass loss on heating for all radiation-damaged pyrochlores (Panda Hill ca. 1%, Blue River ca. 1.5%, Miass ca. 2.9%). [ABSTRACT FROM AUTHOR]

Reflectance spectroscopy in the visible to short-wave infrared regions (500 to 2500 nm) was carried out using natural samples of the rare earth element (REE) phosphate minerals monazite, xenotime, and britholite. Samples were characterized by scanning electron microscopy and electron microprobe analysis. Absorption band positions were recorded with their probable origins, and spectral variability among the samples is discussed. Spectral features of these minerals are driven primarily by 4f-4f intraconfigurational electronic transitions of trivalent lanthanides. The distinct REE distributions of monazite, xenotime, and britholite drive their bulk spectral patterns, which in turn are sufficiently distinct to enable spectral classification. Spectral variability of some specific REE-related absorptions are interpreted to be driven by differences of the coordination polyhedra for the lanthanide cations between the crystal structures. Spectra of these minerals were also compared against carbonatitehosted REE bearing fluorapatite. The work presented here strengthens the growing foundation for the interpretation of reflectance spectra of these REE phosphate minerals and enables exploitation of the observed features by the remote sensing community for detection, identification, and quantification of REE phosphate minerals. This is especially relevant for hyperspectral imaging spectroscopy with high spatial resolution, where the spectral response of a pixel becomes increasingly dominated by mineralogy. [ABSTRACT FROM AUTHOR]

The system B2O3-Al2O3-SiO2 (BAS) includes two ternary phases occurring naturally, boromullite, Al9BSi2O19, and boralsilite, Al16B6Si2O37, as well as synthetic compounds structurally related to mullite. The new mineral vránaite, a third naturally occurring anhydrous ternary BAS phase, is found with albite and K-feldspar as a breakdown product of spodumene in the elbaite-subtype Manjaka granitic pegmatite, Sahatany Valley, Madagascar. Boralsilite also occurs in this association, although separately from vránaite; both minerals form rare aggregates of subparallel prisms up to 100 µm long. Optically, vránaite is biaxial (-), nα = 1.607(1), nβ = 1.634(1), nγ = 1.637(1) (white light), 2Vx(calc) = 36.4°, X ≈ c; Y ≈ a; Z = b. An averaged analysis by EMP and LA-ICP-MS (Li, Be) gives (wt%) SiO2 20.24, B2O3 11.73, Al2O3 64.77, BeO 1.03, MnO 0.01, FeO 0.13, Li2O 1.40, Sum 99.31. Raman spectroscopy in the 3000-4000 cm-1 region rules out the presence of significant OH or H2O. Vránaite is monoclinic, space group I2/m, a = 10.3832(12), b = 5.6682(7), c = 10.8228(12) Å, β = 90.106(11)°; V = 636.97(13) ų, Z = 1. In the structure [R1 = 0.0416 for 550 Fo > 4σFo], chains of AlO6 octahedra run parallel to [010] and are cross-linked by Si2O7 disilicate groups, BO3 triangles, and clusters of AlO4 and two AlO5 polyhedra. Two Al positions with fivefold coordination, Al4 and Al5, are too close to one another to be occupied simultaneously; their refined site-occupancy factors are 54% and 20% occupancy, respectively. Al5 is fivefold-coordinated Al when the Al9 site and both O9 sites are occupied, a situation giving a reasonable structure model as it explains why occupancies of the Al5 and O9 sites are almost equal. Bond valence calculations for the Al4 site suggest Li is likely to be sited here, whereas Be is most probably at the Al5 site. One of the nine O sites is only 20% occupied; this O9 site completes the coordination of the Al5 site and is located at the fourth corner of what could be a partially occupied BO4 tetrahedron, in which case the B site is shifted out of the plane of the BO3 triangle. However, this shift remains an inference as we have no evidence for a split position of the B atom. If all sites were filled (Al4 and Al5 to 50%), the formula becomes Al16B4Si4O38, close to Li1.08Be0.47Fe0.02Al14.65B3.89Si3.88O36.62 calculated from the analyses assuming cations sum to 24. The compatibility index based on the Gladstone-Dale relationship is 0.001 ("superior"). Assemblages with vránaite and boralsilite are inferred to represent initial reaction products of a residual liquid rich in Li, Be, Na, K, and B during a pressure and chemical quench, but at low H2O activities due to early melt contamination by carbonate in the host rocks. The two BAS phases are interpreted to have crystallized metastably in lieu of dumortierite in accordance with Ostwald Step Rule, possibly first as "boron mullite," then as monoclinic phases. The presence of such metastable phases is suggestive that pegmatites crystallize, at least partially, by disequilibrium processes, with significant undercooling, and at high viscosities, which limit diffusion rates. [ABSTRACT FROM AUTHOR]

This study provides new insights into the relation between thermally induced structural reorganization and the macroscopic mechanical properties of radiation-damaged titanite. The natural sample contains ca. 30% amorphous fraction. Low-temperature annealing affects only slightly the sample stiffness and leads to a softening resulting from the defect annihilation in crystalline regions. In the high-temperature annealing regime, amorphous domains recrystallize and this leads to further recovery of defects, reduction of interfaces, grain growth, and, in general, an increase in the long-range order. The thermally induced recrystallization is accompanied by massive dehydration leading to considerable stiffening and hardening. This interpretation of the recrystallization process in titanite based on the correlation of new results from nanoindentation and Raman-spectroscopic measurements complementing previous investigations using thermogravimetric and gas analyses by Hawthorne et al. (1991) and infrared spectroscopy by Zhang et al. (2001). The new data combined with previous work leads to a detailed description of the annealing behavior of a radiation-damaged titanite, which is a complicated process that includes dehydration and atomic-scale structural reorganization. To minimize the influence of surface phenomena on the hardness measurements, the so-called "true" hardness was used instead of the standard hardness calculation (Oliver and Pharr 1992). A comparison shows that the Oliver and Pharr method clearly underestimates the hardness. [ABSTRACT FROM AUTHOR]

Metamict titanite from the Cardiff uranium mine (M28696) in Ontario, Canada, has been analyzed using 29Si magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). A broad Gaussian shaped NMR signal at -81 ppm occurs at room temperature resulting from the mainly locally ordered metamict structural state. NMR signals were obtained at room temperature and after annealing at 600, 950, 1220 and 1470 K. Because of increasing crystallinity the full width at half maximum (FWHM) decreased from 24 ppm to 20 ppm, respectively using a pseudo-Voigt fit. For comparison highly-crystalline titanite from Rauris showed an NMR signal at -79.3 ppm with FWHM of 4.1 ppm and an almost Lorentzian profile because of its good long range order. Integrating synchrotron X-ray diffraction (XRD) signals of Cardiff titanite show an increase of the crystallographic long range order at annealing temperatures considerably lower than the local ordering seen by NMR. [ABSTRACT FROM AUTHOR]

An understanding of the mineralogy and petrogenesis of rare earth element deposits has significant implications for their economic viability. Lanthanide-bearing compounds are known to produce sharp absorption features in the visible to short-wave infrared region (VIS-SWIR), however, a significant knowledge gap exists between the fields of hyperspectral reflectance spectroscopy and rare earth element mineralogy. Reflectance spectra were collected from four bastnäsite samples, two parisite samples, and one synchysite sample from the visible into the short-wave infrared. These REE fluorocarbonate mineral samples were characterized via scanning electron microscopy and electron probe microanalysis. Sharp absorptions of REE-bearing minerals are mostly the result of 4f-4f intraconfigurational electron transitions and for the light REE-enriched fluorocarbonates, the bulk of the features can be ascribed to Nd3+, Pr3+, Sm3+, and Eu3+. The lanthanide-related spectral responses of the REE fluorocarbonates are consistent across the group, supporting the notion that the REE cation site is very similar in each of these minerals. Carbonate-related spectral responses differed between these minerals, supporting the notion that the crystallographic sites for the carbonate radical differ between bastnäsite, synchysite, and parisite. Exploitable spectral differences include a distinct absorption band at 2243 nm that separates bastnäsite from synchysite and parisite. Similarly, for bastnäsite a dominantly Pr3+-related absorption band located is at 1968 nm, while in synchysite and parisite it occurs at 1961 nm. [ABSTRACT FROM AUTHOR]

Green vesuvianite crystals occur with garnet and calcite in a hand specimen from the Nedvědice marble near Kozlov (near Štěpánov nad Svratkou, Svratka Crystalline Complex) in the Czech Republic. The average electron microprobe composition of the vesuvianite shows 12.10 wt% Fe2O3 (4.66 Fe pfu), 2.77 wt% B2O3 (2.45 B pfu), 1.71 wt% As2O5 (0.46 As pfu), and 1.40 wt% F (2.26 F pfu). The Fe concentration is the highest ever recorded for a vesuvianite-group mineral. The boron contents are extremely variable and two of the five compositions show more than the 2.50 B pfu needed for wiluite, and the average is only slightly less than this. The crystal structure [a = 15.7250(4), c = 11.7736(3) Å was refined in space group P4/nnc to an R1 value of 0.0221. The site refinement and Mössbauer spectroscopy results show Fe2+ substituting for Ca at the X3 site and filling the Y1 position, and Fe3+ substituting for Al at the Y3 position. Most of the Fe (70% from the site refinements and 78% from the Mössbauer interpretation) is ferric. The main effect of the high-Fe concentration is to increase the mean Y3-O distance to an unusually large 2.018 Å. Boron occurs at the T1 site, where it is coordinated by oxygen atoms at two O7B and two O11 positions, and at the T2 sites where it is coordinated by O atoms at one O10 and two O12A sites. When the nearby X3 site contains Fe, the T2 position is either vacant or [3]-coordinated by some combination involving an O10 site and two O12B positions, in which case the B atom is likely offset from the T2 site to reduce the B-O12B distance. Fluorine and OH occupy the O11 positions when there is a vacancy at the adjacent T1 position. Pentavalent As substitutes for Si at the Z2 site and Al at the Y2 site. The P4/nnc symmetry indicates that this vesuvianite formed at high temperatures (400-800 °C) and the predominance of Fe3+ and As5+ suggests under oxidizing conditions. The results showing Fe at three different sites with three different coordinations attests to the flexibility of the vesuvianite crystal structure. The incorporation of As at two different sites in the structure shows that rock-forming silicate minerals such as vesuvianite can be a reservoir for this heavy element [ABSTRACT FROM AUTHOR]

Brunogeierite is a rare Ge-mineral with a spinel-type structure. Inconsistences in the brunogeierite formula suggesting divalent germanium in its structure have occurred since its description. A review of the published data and bond-valence calculations show that the correct ideal end-member formula of brunogeierite is (Fe2+)2Ge2+O4. The mineral is newly classified as a nesogermanate member of the ringwoodite group (Strunz classification 9.AC.15). Formal correction of the brunogeierite formula and classification was approved by the IMA Commission on New Minerals, Nomenclature and Classification (IMA-CNMNC) as proposal IMA 11-A. In order to perform bond-valence calculations using divalent germanium, new bond-valence parameters for Ge2+-O (R0 = 1.778 Å, B = 0.37 A) and Ge2+-CI (R0 = 2.156 Å, B = 0.37 Å) were evaluated. [ABSTRACT FROM AUTHOR]

Oxy-schorl (IMA 2011-011), ideally Na(Fe2+2Al)Al6Si6O18(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup, is described. In Zlatá Idka, Slovak Republic (type locality), fan-shaped aggregates of greenish black acicular crystals ranging up to 2 cm in size, forming aggregates up to 3.5 cm thick were found in extensively metasomatically altered metarhyolite pyroclastics with Qtz+Ab+Ms. In Přibyslavice, Czech Republic (co-type locality), abundant brownish black subhedral, columnar crystals of oxy-schorl, up to 1 cm in size, arranged in thin layers, or irregular clusters up to 5 cm in diameter, occur in a foliated muscovite-tourmaline orthogneiss associated with Kfs+Ab+Qtz+Ms+Bt+Grt. Oxy-schorl from both localities has a Mohs hardness of 7 with no observable cleavage and parting. The measured and calculated densities are 3.17(2) and 3.208 g/cm3 (Zlatá Idka) and 3.19(1) and 3.198 g/cm3 (Přibyslavice), respectively. In plane-polarized light, oxy-schorl is pleochroic; O = green to bluish-green, E = pale yellowish to nearly colorless (Zlatá Idka) and O = dark grayish-green, E = pale brown (Přibyslavice), uniaxial negative, ω = 1.663(2), ε = 1.641(2) (Zlatá Idka) and ω = 1.662(2), ε = 1.637(2) (Přibyslavice). Oxy-schorl is trigonal, space group R3m, Z = 3, a = 15.916(3) Å, c = 7.107(1) Å, V = 1559.1(4) Å3 (Zlatá Idka) and a = 15.985(1) Å, c = 7.154(1) Å, V = 1583.1(2) Å3 (Přibyslavice). The composition (average of 5 electron microprobe analyses from Zlatá Idka and 5 from Přibyslavice) is (in wt%): SiO2 33.85 (34.57), TiO2 <0.05 (0.72), Al2O3 39.08 (33.55), Fe2O3 not determined (0.61), FeO 11.59 (13.07), MnO <0.06 (0.10), MgO 0.04 (0.74), CaO 0.30 (0.09), Na2O 1.67 (1.76), K2O <0.02 (0.03), F 0.26 (0.56), Cl 0.01 (<0.01), B2O3 (calc.) 10.39 (10.11), H2O (from the crystal-structure refinement) 2.92 (2.72), sum 99.29 (98.41) for Zlatá Idka and Přibyslavice (in parentheses). A combination of EMPA, Mössbauer spectroscopy, and crystal-structure refinement yields empirical formulas (Na0.591Ca0.103⇔0.306)Σ1.000(Al1.885Fe2+1.108Mn0.005Ti0.002)Σ3.000(Al5.428Mg0.572)Σ6.000(Si5.506Al0.494)Σ6.000O18 (BO3)3(OH)3(O0.625OH0.236F0.136Cl0.003)Σ1.000 for Zlatá Idka, and (Na0.586Ca0.017K0.006⇔0.391)Σ1.000(Fe2+1.879Mn0.015 Al1.013Ti0.093)Σ3.00(Al5.732Mg0.190Fe3+0.078)Σ6.000(Si5.944Al0.056)Σ6.000O18(BO3)3(OH)3(O0.579F0.307OH0.115)Σ1.000 for Přibyslavice. Oxy-schorl is derived from schorl end-member by the AlOFe-1(OH)-1 substitution. The studied crystals of oxy-schorl represent two distinct ordering mechanisms: disorder of R2+ and R3+ cations in octahedral sites and all O ordered in the W site (Zlatá Idka), and R2+ and R3+ cations ordered in the Y and Z sites and O disordered in the V and W sites (Přibyslavice). [ABSTRACT FROM AUTHOR]

Red vesuvianite crystals occur with hausmanite and calcite in a hand specimen from Långban, Sweden. Backscattered electron imaging revealed that a very few of the vesuvianite crystals exhibit cores of higher average atomic number (vesuvianite I) than the bulk (vesuvianite II). Average electron microprobe compositions of vesuvianite I show 3.32 wt% MnO (1.43 Mn2+ apfu), 3.13 wt% Bi2O3 (0.41 Bi3+ apfu), 0.82 wt% Cl (0.71 Cl apfu), and 0.56 wt% As2O5 (0.15 As5+ apfu). The average vesuvianite II composition shows considerably more Mn (4.14 wt% MnO, or 1.76 Mn2+ apfu) but less Bi (0.62 wt% Bi2O3, or 0.08 Bi3+ apfu) and Cl (0.13 wt% Cl, or 0.11 Cl apfu) and about the same amount of As (0.62 wt% As2O5, or 0.16 As5+ apfu). The crystal structures of vesuvianite I (a = 15.595, c = 11.779 Å) and II (a = 15.585, c = 11.778 Å) were refined in space group P4/nnc to R1 values of 0.0445 and 0.0167, respectively. The results show Bi at the new Bi3 position and Cl at the new Cl site; Bi3 can only be occupied when there is a vacancy at the nearby (~0.4 Å) X3 position, and Cl when there is a vacancy at the nearby (~0.4-0.5 Å) O10 position. Bond distances and site occupancies suggest that the Cl atom at the Cl site is bonded to the Bi atom at the Bi3 position when it is occupied. Arsenic occupies the T1 site and is coordinated by oxygen atoms at two O7B and two O11 positions. Manganese replaces Ca at the X1 and X2 position and dominates the Y1 position in vesuvianite I, whereas in vesuvianite II it replaces Ca at the X1 site and fills the Y1A position. In both structures Mn also occurs subordinate to Al + Mg at the Y3 position. Bond-valence analysis indicates that the Mn at the Y1 and Y1A positions is divalent rather than trivalent as required for manganvesuvianite. [ABSTRACT FROM AUTHOR]

The structural state of metamict titanite was studied by Raman spectroscopy, complementary high-resolution transmission electron microscopy, and single-crystal X-ray diffraction. The results show that Raman scattering collected from metamict titanite is highly anisotropic, which is typical of single crystals. But surprisingly, the observed Raman-scattering dependence on the sample orientation is much more pronounced for heavily metamict than for weakly metamict titanite samples. These radiation-induced anisotropic effects are related to the specific atomic arrangements in metamict titanite. The Raman spectra collected in backscattering geometry from a plane nearly perpendicular to the chains of corner-sharing TiO6 octahedra arise predominantly from phonon modes in crystalline nanoregions with radiation-induced defects, whereas the contribution of atomic vibrations in radiation-induced amorphous nanoregions is better pronounced in the Raman spectra collected from a plane containing TiO6 chains. This difference provides a unique opportunity to study separately, the structural transformations of the crystalline and amorphous fractions in metamict titanite. The results show that the radiation-induced periodic faults in the crystalline matrix are related to the disturbance of SiO4-TiO6-SiO4-TiO6 rings comprising TiO6 octahedra from different chains, whereas the radiation-induced amorphization is related to the partial change of Ti coordination from octahedral to pyramidal and/or tetrahedral, which in turn violates the Ti-O-Ti intrachain linkages. This indicates that the plane containing Si-O-Ti-O bond rings is less susceptible to a self-accumulation of radiation-induced defects resulting in the development of amorphous regions as compared to the perpendicular plane containing Ti-O bond chains. Sample-orientation-dependent Raman spectroscopy was further applied to annealed metamict titanite to give further insight into the temperature-driven recovery processes in the crystalline and amorphous nanoregions. Multistep annealing by 50 K for 2 h per step gradually suppresses the structural defects in the crystalline fraction as the improvement of the SiO4-TiO6 connectivity within planes nearly perpendicular to the TiO6 chains reaches saturation near 900 K. The annealing-induced recrystallization of the radiation-induced amorphous nanoregions takes place in the temperature range between approximately 650 and 950 K, with a maximum near 750 K. Raman scattering shows that multistep annealing up to 1173 K is insufficient to recover the crystalline structure of the studied metamict titanite sample, which has an accumulated radiation dose of 1.2 x 1018 α-event/g. [ABSTRACT FROM AUTHOR]

Three samples from the dumortierite group of minerals were examined with magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR): a dumortierite [c. (Al,□)Al6(BO3) Si3O13(O,OH)2] consisting of dark blue euhedral crystals from Madagascar (D34); a fine-grained pale blue dumortierite from Island Copper mine, British Columbia, Canada (D12); and a creamy white holtite [c. (Ta,Nb,□,Al)Al6(BO3)(Si,Sb,As)3O12 (O,OH,□)3] from Szklary, Lower Silesia, Poland (WPH). Restricted Hartree-Fock ab initio electronic structure calculations were performed on model clusters with the goal of matching local environments of Si atoms to peaks in the 29Si MAS NMR spectra. The spectrum of D34 showed five resolved peaks at -95.2, -92.6, -91.3, -89.1, and -86.5 ppm with deconvoluted peak area contributions of 57,19,7,10, and 7%. Electronic structure calculations, cross-polarization MAS NMR measurements and relative intensities support assigning the peaks at -95.2 and -92.6 ppm to Si2 and Si1 sites, respectively, adjacent to fully occupied Al1 sites (i.e., Q4 Si sites), and assigning the three remaining peaks to Si sites adjacent to vacant Al1 sites (i.e., Q³ Si sites). Due to the complexity of the dumortierite structure, clusters composed of at least the first four shells of nearest neighbor atoms to the target Si atom are necessary to model Q4 sites. The spectrum of D12 showed two main peaks at -93 and -95 ppm, with minor peaks below -90 ppm and above -100 ppm. The spectrum of WPH showed one broad peak at-93 ppm, likely containing both Si1 and Si2 signals, and two minor peaks below -90 ppm. Single-crystal X-ray diffraction and structure refinement on D34 shows orthorhombic symmetry, Pnma, Z = 4,a = 4.6882(1), b = 11.7924(2), c = 20.1856(3) Å, and V = 1115.97(4) ų with R1 = 0.0124. Three distinct sub-sites of the face-sharing octahedral chain site Al1 were distinguished corresponding to sites with one vacancy above, with one vacancy below, and between two occupied sites; the vacancy-adjacent sites have the cation displaced to increase the A13+-Al3+ distance. Each sub-site is approximately ¼ occupied, suggesting that A13+ cations in individual face-sharing octahedral chains are ordered as □-A1-A1-A1, although cations from chain to chain are disordered, preserving Pnma symmetry. Powder X-ray diffraction measurements were performed on both D34 and D12. The unit cell of D12 was found to be a = 4.7001(7), b = 11.785(2), c = 20.277(3) Å. [ABSTRACT FROM AUTHOR]

We have measured the elastic response of radiation-damaged titanite, CaTiSiO5, as a function of thermal annealing. We estimate the bulk modulus of the damaged samples (~24% amorphous) to be 85 GPa, which is much softer than for undamaged crystalline titanite [131.4 GPa; Angel et al. (1999)]. Conversely, the lowest shear modulus of the radiation-damaged material is 52-58 GPa, which is harder that of the undamaged titanite, 46-52 GPa. The bulk and shear moduli of the radiation-damaged materials are close to those of thermal titanite glass, Bglass ≈ 75 GPa and Gglass ≈ 47 GPa, and are much smaller than expected based on other radiation-damaged materials such as zircon (ZrSiO4). Surprisingly, annealing of the damaged titanite in the range 600 < T < 1000 K leads to additional massive softening of the shear moduli. During annealing the shear modulus of titanite sample 1 softened from 58 to 29 GPa, and sample 2 softened from 52 to 19 GPa. The temperature range for the softening coincides with that found for crystallization of the amorphous regions, as measured previously by diffraction and spectroscopic methods. In contrast to the huge softening of the ultrasonically measured shear modulus, the calorimetrically measured Debye temperature θD increases by ~5%, suggesting a small intrinsic hardening of the acoustic shear modes. Additional heating to 1473 K leads, in one titanite sample, to a steep increase of the shear modulus to values much larger than that of the initial, radiation-damaged material. Theoretical models are discussed to rationalize the massive softening due to both radiation damage and subsequent anneal. [ABSTRACT FROM AUTHOR]

Dark blue aquamarine was discovered in the Yukon Territory in 2003. The crystals occur in a swarm of quartz ± siderite ± fluorite ± allanite veins that fill tension gashes in a syenite stock. Previous studies suggest a metamorphic origin for the mineralizing fluid and local derivation of vein constituents. The dark blue beryl contains nearly 6.0 wt.% iron oxide and the colour is thought to be due to intervalence charge-transfer between Fe2+ and Fe3+ cations. Five stones weighing up to 0.82 carat were faceted in 2003, but these are heavily fractured and included. However, many of the smaller crystals discovered to date are transparent. [ABSTRACT FROM AUTHOR]

The electron microprobe compositions and crystal structure of seven members of the grandidieriteominelite (MgAl3BSiO9.Fe2+Al3BSiO9) series with X = (Fe2+ + Mn + Zn)/(Fe2+ + Mn + Zn + Mg) ranging from 0.00 to 0.52 were studied to determine the geometric effects of Fe substitution for Mg on the crystal structures. Calculating Fe3+ from the electron microprobe analyses gave 0.04.0.06 Fe3+ apfu, but such small amounts at the Al sites could not be detected in the refinements. Regression equations derived from single-crystal X-ray diffraction data show that b increases by 0.18 Å from X = 0.1. The crystal structure refinements show that the most significant changes involve the (Mg,Fe2+)O5 polyhedron, which increases in volume by 0.36 ų (5.0%), largely as a result of expansion of the MgFeO5, -O2, and -O6 (x2) bond distances, which increase by 0.09 (4.4%), 0.06, and 0.04 Å, respectively. Other significant changes include increasing O1-MgFe-O2 (3.44°) and -Al3-O5a angles (1.9°) and a decreasing O6-MgFe-O6b (.2.20°) angle. Significant increases are also seen in the lengths of the O1-O2 (0.13 Å) and O6-O5a (x2) (0.09 Å) edges. The SiO4 tetrahedra appear to respond to changes in the surrounding polyhedra by changing O-Si-O angles such that the tetrahedral angle variance and mean tetrahedral quadratic elongation increase with X. The BO3 triangles appear to behave as relatively invariant units in the crystal structure. Regression equations obtained from the MgFe-O bond distances were used to determine a radius for VFe2+ of 0.70 Å. Although our samples show little Mn, the presence of Mn2+ at the MgFe site would be expected to cause more distortion than an equivalent amount of Fe2+. Substitution of Zn likely would have little effect. The presence of Cr3+ at any of the Al sites would be expected to increase the size of the coordination sphere, but the substitution of P5+ for Si at the Si sites would most likely decrease the Si-O bond distances. [ABSTRACT FROM AUTHOR]