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The role of the oxo-component on the compressibility of amphibole was studied by means of high-pressure in situ single-crystal X-ray diffraction on two natural kaersutite megacrysts (samples DL5 and FR12) from alkaline basalts. The oxo-component varies significantly (1.1 and 1.9 apfu in DL5 and FR12, respectively), whereas the cation composition is very similar, apart from the [Fe.sup.3+]/([Fe.sup.2+][Fe.sup.3+]), which is 0.33 in DL5 and ~1 in FR12. The larger oxo-component of FR12 is attributed to the [Fe.sup.2+] + O[H.sup.-] = [Fe.sup.3+] + [O.sup.2-] + 1/2[H.sub.2] substitution. Unit-cell parameters were collected at different pressures up to about 8 GPa. Structural refinements of both samples were performed with data collected at different P up to 6 GPa. Fitting the P-V data to a third-order Birch Murnaghan EoS yielded the following parameters: [K.sub.0] = 94(1) GPa, K' = 6.3(4), and [V.sub.0] = 903.6(2) [[Angstrom].sup.3] for FR12 and [K.sub.0] = 91(2) GPa, K' = 6.2(4), and [V.sub.0] = 914.1(2) [[Angstrom].sup.3] for DL5. The axial moduli of the two amphibole samples were: [K.sub.0a] = 86(3) GPa, [K'.sub.a] = 7(1), and [a.sub.0] = 9.815(2) [Angstrom]; [K.sub.0b] = 115(3) GPa, [K'.sub.b] = 4.8(8), and [b.sub.0] = 18.012(2) [Angstrom]; [K.sub.0c] = 112(5) GPa, [K'.sub.c] = 7(1), and [c.sub.0] = 5.300(1) [Angstrom], for sample FR12 and [K.sub.0a] = 85(3) GPa, [K'.sub.a] = 5(1), and [a.sub.0] = 9.8660(9) [Angstrom]; [K.sub.0b] = 113(2), [K'.sub.b] = 4.4(6), and [b.sub.0] = 18.0548(6) [Angstrom]; [K.sub.0c] = 107(3) GPa, [K'.sub.c] = 7(1), and [c.sub.0] = 5.3185(5) [Angstrom], for sample DL5. This suggests that the compressibility of kaersutite decreases with increasing oxo-component. Structural refinements show that the polyhedral compressibility follows the order A = M4 > M2 > M3 > M1 for DL5 andA = M4 > M2 > M1 > M3 for FR12. The most evident geometrical effect induced by P is the decrease in the bending of the double tetrahedral chain, when adjacent I-beams are pushed against each other. This effect is largest for DL5, which has a larger concavity of the A site, (O7-O7' changes from 3.03 to 2.82 [Angstrom]) compared to the one of FR12, (O7-O7' changes from 2.92 to 2.79 [Angstrom]). This mechanism is confirmed by the evolution of T1-O7-T1 angle (from 135.4[degrees] to 132.5[degrees] in FR12 and from 136.6[degrees] to 132.2[degrees] in DL5). Keywords: Oxo-amphiboles, kaersutite, compressibility, equation of state, high-pressure structure, amphibole DOI: 10.2138/am.2010.3429

We present the results of a single-crystal X-ray diffraction structural study on pyroxmangite in a diamond-anvil cell up to 5.6 GPa. The sample comes from Yokone-Yama, Awano Town, Tochigi Prefecture, Japan. Crystals are triclinic, centrosymmetric, with composition [[Mn.sub.0.576(2)][Fe.sub.0.284(5)][Ca.sub.0.044(3)] [Mg.sub.0.089(2)]][Si.sub.1.003(4)][O.sub.3]. Structure refinements were performed with intensity data collected at 1.24 and 3.57 GPa on a CCD-equipped diffractometer. Lattice parameters were accurately measured with the point-detector mounted on the same instrument. The bulk modulus of pyroxmangite fitting data to a second-order Birch-Murnaghan equation of state is [K.sub.0]= 109.6(7) GPa. Axial compressibility values were [[beta].sub.a]= 2.2(1), [[beta].sub.b]= 3.3(1), and [[beta].sub.c] 2.6(1) [10.sup.-3] G[Pa.sup.-1] showing slightly anisotropic behavior, with the most compressible direction along the b axis, as commonly found in the related family of pyroxene. Silicon tetrahedra are almost incompressible in the pressure range investigated. M polyhedra are more compressible: the volume change is smaller in the more regular octahedra M1-M4 (-3.3%) and greater in the more irregular polyhedra M5-M7 (-5.2%). Owing to the different contraction of Si tetrahedra and cation polyhedra, the sevenfold tetrahedral chains in pyroxmangite must kink to avoid misfit between chains and octahedral bands. This results in shortening of 1.2% of the c axis and a decrease in both [O.sub.br] -[O.sub.br]-[O.sub.br] and Si-[O.sub.br]-Si angles. The behavior of pyroxmangite at high P is approximately inverse to that observed at high T. Compressibility data may be combined with those on thermal expansion to formulate the approximate equation of state: V = [V.sub.0] (1 - 9.12 x [10.sup.-3] [DELTA]P + 3.26 x [10.sup.-5] [DELTA]T), where P is in GPa and T in degrees Celsius. Keywords: Pyroxmangite, pyroxenoid, equation of state, compressibility

A single-crystal X-ray diffraction study in a diamond anvil cell up to 5.41 GPa was carried out on a clinochlore [monoclinic polytype IIb-2, S.G. C2/m, ([Mg.sub.9.09][F.sup.2+.sub.1.01][Mn.sub.0.02][Ti.sub.0.01] [Cr.sub.0.02][Al.sub.1.80])[SIGMA] = 11.95 ([Si.sub.6.35] [Al.sub.1.65])[SIGMA] = 8 [O.sub.20][(OH).sub.16] from Val Malenco, Italy. The bulk modulus of monoclinic clinochlore calculated by fitting unit-cell volumes and pressures to a third-order Birch-Murnaghan Equation of State (EoS), is [K.sub.0] = 71(9) GPa with K' = 8(5). Axial compressibility values were [[beta].sup.EoS.sub.0a] = 3.8(1), [[beta].sup.EoS.sub.0b], [[beta].sup.EoS.sub.0a] = 5.4(5) [10.sup.3] GP[a.sup.-1], showing that axial anisotropy is much less than that found for other phyllosilicates. Compressibility data are in fair agreement with literature data, which are based on powder neutron and synchrotron diffraction methods. Results were compared with the behavior of the triclinic polytype of similar composition and coexisting in the same rock. Symmetry has little overall influence on compressibility, but compared with the triclinic polytype of similar composition and coexisting in the same hand specimen, the monoclinic polytype is slightly less rigid. Comparison of structural refinements at different pressures showed that structural deformations mainly affect the interlayer region, where hydrogen bonds are important for the structural properties of the phase. The mean decrease in OH-O distances was about 9% in the pressure range 0-5 GPa. Structural behavior was very similar to that found for the triclinic polytype. Although energy differences between polytypes are relatively small, their compressional behavior may have implications in terms of relative stability. A computation of molar volume applying an isothermal EoS shows that the triclinic polytype is lower in volume up to 0.9 GPa, above which the volume of the monoclinic phase is smaller. This fact gives information on the relative stability of the two polytypes and a possible explanation for the greater abundance of the triclinic polytype in low to medium-P environments, as is commonly observed in nature. Keywords: Chlorite, high pressure, polytypism, equation of state

We present the results of a single-crystal X-ray diffraction structural study of chlorite in a diamond anvil cell up to 5.47 GPa. The sample is a clinochlore from Val Malenco, Italy, triclinic polytype IIb-4, S.G. C[bar.1]], with pseudomonoclinic metric and composition [([Mg.sub.9.14][Fe.sup.2+.sub.1.02][Fe.sup.3+.sub.0.01] [Mn.sub.0.01] [Ti.sub.0.01][Al.sub.1.76]).sub.[summation]=11.95][([Si.sub.6.32] [Al.sub.1.68]).sub.[summation]=8][O.sub.20][(OH).sub.16]. Structural refinements were performed at several pressures with intensity data collected on a CCD diffractometer. Unit-cell parameters were accurately measured with the point-detector mounted on the same instrument. The bulk modulus of chlorite fitting data to a third-order Birch-Murnaghan equation of state is [K.sub.0]. = 88(5) GPa with K' = 5(3). Results are in fair agreement with data based on powder neutron and synchrotron diffraction methods. The axial compressibility values were [[beta].sup.EoS.sub.0a] = 3.4(2), [[beta].sup.EoS.sub.0b] = 3.4(1), and [[beta].sup.EoS.sub.0c] = 5.4(2) [10.sup.-3] [GPa.sup.-1]. The metric of the lattice remains triclinic in the investigated pressure range. Axial anisotropy is strongly reduced with respect to the axial compressibilities observed in other phyllosilicates. Comparison of structural refinements at different pressures shows that the main structural deformations affect the interlayer region, where the hydrogen bonds are relevant to the structural properties of the phase. The mean decrease of the OH-O distances is about 10% from ambient pressure to ~5 GPa. Compressibility data may be combined with those on thermal expansion to formulate an equation of state for clinochlore. Taking into account the thermal expansion coefficient reported in literature for a chlorite with a composition quite similar to that of our sample, we can write the equation: V = [V.sub.0] (1 - 1.14 [10.sup.-2] [DELTA]P + 2.316 [10.sup.-5] [DELTA]T), where P is in GPa and T in Celsius. Assuming an average rock density of 2.7 g/[cm.sup.3], this corresponds to an isochoric P-T geothermal gradient of 18 [degrees]C/km. Keywords: Chlorite, compressibility, equation of state, high pressure

Here we report the results of the first three-dimensional refinement of the 10 [Angstrom] phase performed with single-crystal X-ray data. The 10 [Angstrom] phase, [Mg.sub.3][Si.sub.4][O.sub.10][(OH).sub.2] [H.sub.2]O, is monoclinic, space group C2/m, a = 5.323(1)[Angstrom], b = 9.203(1)[Angstrom], c = 10.216(1)[Angstrom], [beta] = 99.98(1) [degrees], V= 492.9(2) [[Angstrom].sup.3]; the calculated density, assuming Z = 2, is 2.676 g.[cm.sup.-3]. The structure has been solved by direct methods and refined by least-squares method with anisotropic displacement parameters. The final agreement index ([R.sub.1]) was 0.088 for 54 refined parameters and 499 unique observed reflections collected with a diffractometer with a CCD detector. The structure of the 10 [Angstrom] phase is very similar to that of a homo-octahedral, 1 M trioctahedral mica: it is a silicate consisting of 2:1 tetrahedral-octahedral layers parallel to (001). The mean Si-O, Mg1-O, and Mg2-O bond lengths are 1.626, 2.082, and 2.081 [Angstrom], respectively. The ditrigonal rotation angle [alpha] is 0.53[degrees]. The interlayer of the 10 [Angstrom] phase is occupied by water molecules. According to the oxygen occupancy, 1 [H.sub.2]O p.f.u, is assumed in the investigated sample. Although the average water oxygen position is in the mid-plane, structural refinement suggests disorder along c*. Twelve hydrogen bonds are located between the water molecule and the 6 + 6 oxygen atoms of the basal rings of adjacent tetrahedral sheets (water-oxygen distances averaging 3.19 [Angstrom]). Therefore there are six possible orientations for the water molecule, with six hydrogen bonds pointing toward the upper basal ring and six pointing toward the lower ring of tetrahedral sheets. The orientational disorder of water, in agreement with previous Raman spectroscopy data, is a feature relevant to the evaluation of thermodynamic functions and thermal stability of the 10 [Angstrom] phase, which is a possible water carrier (9.1 wt%) in subducting slabs at high pressure.

The structural behavior of phlogopite was studied by in situ single-crystal X-ray diffraction (XRD) in a diamond-anvil cell, using crystals of composition [([K.sub.0.091][Na.sub.0.02][Ba.sub.0.03]) ([Fe.sup.2+.sub.0.163][Fe.sup.3+.sub.0.163][Al.sub.0.123][Mg.sub.1.81], [Ti.sub.0.149])[Si.sub.2.708][Al.sub.1.292][O.sub.10][OH.sub.1.725] [F.sub.0.175]]. Lattice parameters were measured from 0.0001 to 6.5 GPa and fitted with a third-order Birch-Murnaghan equation of state (EoS). The resulting EoS parameters are: [V.sub.0] = 497.1(1) [[Angstrom].sup.3], [K.sub.0] = 54(2) GP[a.sup.-1], and K' = 7(1); [a.sub.0] = 5.336(1) [Angstrom], [K.sub.0] = 123(9) GPa, and K' = 3(2); [b.sub.0] = 9.240(3) [Angstrom], [K.sub.0] = 128(15) GPa, and K' = 3(2); [c.sub.0] = 10.237(6), [Armstrong], [K.sub.0] = 25(2) GPa, and K' = 5(1); the [beta] angle increases linearly with pressure from 100.02(5) to 100.4(1)[degrees]. The structural evolution of phlogopite was studied by comparing five structural refinements performed with intensity data collected at 0.0001, 1.2, 3.2, 5.0, and 6.0 GPa. The interlayer site, where K is located, is about 4.5 times more compressible than the T-O-T unit. At the same time, the greater compression of the octahedral layer with respect to the tetrahedral one induces an increase in tetrahedral rotation angle [alpha] from 9.29 to 11.9[degrees]. Structural evolution with pressure yields a crystallographic rationale for the larger baric stability of K-deficient and Si-rich phlogopites, as observed from natural and experimental data. Combined high-pressure and thermal expansion data yield the approximate EoS: V= [V.sub.0](1 + 4.6 x [10.sup.-5][DELTA]T-0.0167 [DELTA]P), where P is in GPa and T in [degrees]C. This equation was used to calculate phase equilibria in lherzolite compositions modeled in the simplified [K.sub.2]0-CaO-MgO-[Al.sub.2][O.sub.3]-Si[O.sub.2]-[H.sub.2]O (KCMASH) system. The results show that the effect of phlogopite on bulk density is particularly significant at high pressure and temperature since, above the chlorite stability field, phlogopite is the only hydrous phase able to lower bulk density properties by about 0.5% with respect to the K-free bearing system.

This paper described a baseline for a multidisciplinary approach to the mineralogical and chemical characterization of eighteen fragments of archaic transport amphoras (7th-6th centuries BC) found at Gravisca archaeological site (Lazio, Italy) attributed to an Eastern Aegean provenance (six from Samos, three from Miletus, three from Chios and three from Klazomenai). The samples have been typed on the evidence concerning archaic manufactory techniques by using X-ray powder diffraction (XRPD) associated with quantitative phase analysis (QPA), optical (OM) and electron microscopy (SEM). Following Inductive Coupled Plasma Spectroscopy (ICP), compositional data analysis has been for the first time applied to selected geochemical proxies combining rare earth elements and selected heavy metals concentration in Hierarchical Agglomerative Cluster (HAC). This innovative approach allows to distinguish different sources of the raw materials used from different geological and geographical areas. Multivariate statistical treatments via Principal Component Analyses (PCA) open the possibility to group the sherds into clusters, comparing the results with the HAC application allowing to validate the methodology. Two distinct centres associated with Samos manufactory appear to be operating during 7th-6th centuries BC, which could be related to different production periods or even different production areas. The new data concur with a more straightforward historical reconstruction of archaic Poleis manufactory and commercial activity toward Etruria and the Mediterranean and with a new methodological approach to archaeometry. [ABSTRACT FROM AUTHOR]