Electron microprobe analyses are presented for fluorapatite phenocrysts from a benmoreite-peralkaline rhyolite volcanic suite from the Kenya Rift Valley. The rocks have previously been well characterized petrographically and their crystallization conditions are reasonably well known. The REE contents in the M site increase towards the rhyolites, with a maximum britholite component of ~35 mol.%. Chondrite-normalized REE patterns are rather flat between La and Sm and then decrease towards Yb. Sodium and Fe occupy up to 1% and 4%, respectively, of the M site. The major coupled substitution is REE3+ + Si4+ ↔ Ca2+ + P5+. The substitution REE3+ + Na+ ↔ 2Ca2+has been of minor importance. The relatively large Fe contents were perhaps facilitated by the low fO2conditions of crystallization. Zoning is ubiquitous and resulted from both fractional crystallization and magma mixing. Apatites in some rhyolites are relatively Y-depleted, perhaps reflecting crystallization from melts which had precipitated zircon. Mineral/glass (melt) ratios for two rhyolites are unusually high, with maxima at Sm (762, 1123).

The crystal structures of twenty-five orthorhombic Fe-Mg-Mn amphiboles, a = 18.525 – 18.620, b = 17.806-18.034, c = 5.264-5.303 Å, V = 1737.6-1776.7, space group = Pnma, Z = 4, have been refined to R indices in the range 2.1–7.8% using 790–1804 unique observed reflections measured with Mo-Kα X-radiation on a Bruker P4 automated four-circle diffractometer equipped with a 1K CCD detector. The quality of the refinements is strongly a function of the [4]Al content of the crystals because of unmixing in the central part of the series due to the presence of a low-temperature solvus. The amphibole crystals were analysed by electron microprobe subsequent to collection of the X-ray intensity data and span the anthophyllite-gedrite series from 0.17–1.82 [4]Al a.p.f.u. Mössbauer spectroscopy shows that the amphiboles of this series commonly contain small but significant amounts of Fe3+ . The amount of [4]Al is linearly related to the grand <T-O> distance by the equation <T-O> = 1.6214 + 0.171 [4]Al, R = 0.980; the slope of this relation is not significantly different from that characteristic of a hard-sphere model. The <T-O> distances indicate the following site preference for [4]Al: T1B > T2B > T1A » T2A. The <M2-O> distances are compatible with all [6]Al and Fe3+ ordered at the M2 site. The grand <M1,2,3 '3 –O> distance is related to the mean radius of the constituent cations, <rM1,2,3>, by the equation ≪M1,2,3-O≫ = 1.4684 + 0.8553(7) <rM1,2,3>.

Minerals isostructural with sapphirine-1A, sapphirine-2M, and surinamite are closely related chain silicates that pose nomenclature problems because of the large number of sites and potential constituents, including several (Be, B, As, Sb) that are rare or absent in other chain silicates. Our recommended nomenclature for the sapphirine group (formerly aenigmatite group) makes extensive use of precedent, but applies the rules to all known natural compositions, with flexibility to allow for yet undiscovered compositions such as those reported in synthetic materials. These minerals are part of a polysomatic series composed of pyroxene or pyroxene-like and spinel modules, and thus we recommend that the sapphirine supergroup should encompass the polysomatic series. The first level in the classification is based on polysome, i.e. each group within the supergroup corresponds to a single polysome. At the second level, the sapphirine group is divided into subgroups according to the occupancy of the two largest M sites, namely, sapphirine (Mg), aenigmatite (Na), and rhönite (Ca). Classification at the third level is based on the occupancy of the smallest M site with most shared edges, M7, at which the dominant cation is most often Ti (aenigmatite, rhönite, makarochkinite), Fe3+ (wilkinsonite, dorrite, høgtuvaite) or Al (sapphirine, khmaralite); much less common is Cr (krinovite) and Sb (welshite). At the fourth level, the two most polymerized T sites are considered together, e.g. ordering of Be at these sites distinguishes høgtuvaite, makarochkinite and khmaralite. Classification at the fifth level is based on XMg = Mg/(Mg + Fe 2+) at the M sites (excluding the two largest and Ml). In principle, this criterion could be expanded to include other divalent cations at these sites, e.g. Mn. To date, most minerals have been found to be either Mg-dominant (XMg > 0.5), or Fe2+-dominant (XMg < 0.5), at these M sites. However, XMg ranges from 1.00 to 0.03 in material described as rhönite, i.e. there are two species present, one Mg-dominant, the other Fe2+-dominant. Three other potentially new species are a Mg-dominant analogue of wilkinsonite, rhönite in the Allende meteorite, which is distinguished from rhonite and dorrite in that Mg rather than Ti or Fe3+ is dominant at Ml, and an Al-dominant analogue of sapphirine, in which Al > Si at the two most polymerized T sites vs. Al < Si in sapphirine. Further splitting of the supergroup based on occupancies other than those specified above is not recommended.

A variety of mushroom tourmaline from the Kat Chay mine, Momeik, near Mogok, Shan state, Myanmar, consists of a black-to-grey single-crystal core from which a single prismatic crystal reaches to the edge of the mushroom, forming a slight protuberance. The rest of the mushroom (∼50% by volume) consists of extremely acicular sub-parallel crystals that diverge toward the edge of the mushroom. The acicular crystals are dominantly colourless to white, with a continuous black zone (2 mm across) near the edge, and pale pink outside the black zone. The composition varies from ∼Na0.75Ca0.05(Li0.80Al0.70Fe1.10.Mn0.30Ti0.10)Al6Si6(B03)3O18(OH)3(OH,F) at the base of the mushroom to ∼Na0.60Ca0.06(Li1.00Al1.98Fe0.02)Al6(Si5.35B0.65)(BO3)3O18(OH)3(OH,F) close to the edge at the top of the mushroom. The principal substitutions are: (1) YLi + YAl -> yFe* + yFe* and (2) TB + yAl -> Si + yFe*, but there are five other minor substitutions that are also operative. There are six significant compositional discontinuities at textural boundaries in the mushroom, suggesting that the changes in habit are driven in part by changes in external variables such as T and P, plus possible involvement of new fluid phases.

Storage of CO2 as solid Ca, Mg, and Fe carbonates in basaltic rocks may provide a long-lasting solution for reduction of industrial CO2 emissions. Here, we report on the underground stratigraphy of the chemical composition and crystallinity of rocks and their alteration state at a targeted field site for injection of CO2-charged waters, the Hellisheidi area in SW Iceland.

Angastonite, ideally CaMgAl2(PO4)2(OH)4-7H2O, is a newly defined mineral from the Penrice marble quarry, South Australia. The mineral occurs as snow-white crusts and coatings up to ∼1 mm thick associated with minyulite, perhamite, crandallite and apatite-(CaF). The streak is white, the lustre is pearly and the estimated hardness is 2 on the Mohs scale. Angastonite forms platy crystals with the forms {010} (prominent), {101}, {101} and {100} (rare), and also occurs as replacements of an unknown pre-existing mineral. There is one cleavage direction on ﹛010} and no twinning has been observed. Angastonite is triclinic, P1̄, with a = 13.303(1) Å, b = 27.020(2) Å, c = 6.1070(7) Å α = 89.64(1)°, β = 83.44(1)°, γ = 80.444(8)°, V = 2150.5(4) Å3, with Z = 6. The mineral is optically biaxial (+), with refractive indices of α = 1.566(2), β = 1.572(2) and γ 1.584(2) and with 2Vmeas = 70(2)° and 2Vcalc = 71°. Orientation: X ≈ a, Y ≈ b, Z ≈ c; with crystals showing parallel extinction and no axial dispersion. Dmeas is 2.47 g/cm3, whilst Dcalc is 2.332 g/cm3. The strongest four powder-diffraction lines [d in Å, (I/I°), hkl] are: 13.38, (100), 020; 11.05, (25), 11̄0; 5.73, (23), 101, 230 and 111; 8.01, (21), 130. Angastonite is likely to be related to the montgomeryite-group members and have a similar crystal structure, based on slabs of phosphate tetrahedra and Al octahedra.

Brachiopods are a phylum of shell-forming sessile marine invertebrates which have existed since the early Cambrian. Two very different biomaterial design strategies for their shells evolved early in their history. Both strategies use hybrid fibre composites, however, one is based on mineral fibres embedded in ~2 wt.% of organic biopolymer sheaths and the inorganic fibres are calcite single crystals. In the second strategy the fibres are biopolymers and are reinforced with Ca-phosphate nanoparticles to form a fibrous nanocomposite. Here the organic component (chitin) dominates. The Ca-phosphate nanoparticle-reinforcement strategy is not unlike that in vertebrate bone, however, the microscale structure is laminated with alternating laminae which have a different degree of mineralization.

The calcitic shells feature an outer compact layer of calcite micro- and nanoparticles protecting the inner fibrous layer from the outside. Transmission electron microscopy of the fibrous layer reveals intercrystalline and intracrystalline biopolymers. The calcitic shell material is stiff with nano-indentation E-moduli of 63±8 GPa and relatively hard (Vickers microhardness up to 400 HV 0.0005/10 and nanohardness 4±0.5 GPa). Compared to inorganic calcite the microhardness is doubled and the nanohardness increases by 60%. We attribute this increased hardness to intracrystalline biopolymers. The nano-indentation E-moduli of the chitinophosphatic shells range from 3 to 55 GPa as a result of the varying degree of mineralization between their laminae, and similarly their nanohardness varies between 0.1 and 3 GPa. For brachiopods burrowing inside the sediment, the alternation of non-mineralized laminae with thin, more strongly mineralized laminae provides abrasion-resistance, hardness and longitudinal stiffness while it preserves the flexibility provided by the organic component for bending movements.

The distribution of Mg and Ni over the octahedrally-coordinated sites M(l,2,3) in Ni-substituted potassic richterite solid solution, AKB(NaCa)c(Mg2.5Ni2.5)Si8O22(OH)2, synthesized at 0.1 GPa/750°C (25 days), has been studied in situ to 700°C by neutron powder diffraction with Rietveld structure refinement. Using a 2.7 g sample it was possible to make short data collections (3 h) at each temperature at intervals of 50° from 50 to700°C and locate the onset of cation exchange. Above 700°C the amphibole decomposes rapidly and so only an on-heating dataset was collected. Unit-cell parameters increase smoothly upon heating, with no discontinuities evident. Site occupancies of M(l), M(2) and M(3) sites were refined from site-scattering values. The initial XNi values of M(l), M(2) and M(3) sites, corresponding to the synthesis temperature of 750°C, are 0.57(1), 0.34(1) and 0.68(2), respectively. Above 400°C, there is initial ordering whereby thermal annealing allows the disordered Mg-Ni distribution of the quenched synthesis product to adjust to be closer to those appropriate for lower temperatures of the heating sequence. This ordering involves the exchange of Mg and Ni between M(l) and M(2), with no significant change in M(3) occupancy. At 700°C, XNi values of the M(l), M(2) and M(3) sites are 0.64(1), 0.27(1) and 0.69(2), respectively. No disordering was observed, due to the short duration of the high-temperature data collections and decomposition at 750°C. The results of this study indicate that divalent cations exchange between octahedral sites in amphiboles in a matter of hours.

The general formula of the amphiboles of this series may be written as NaxMg2(Mg(5-y)Aly,)(Si(8-z)Alz)O22(OH)2, where Mg = Mg + Fe2+ + Mn2+ and Al = Al + Fe3+ + Ti. The individual <T–O> distances are linear functions of their [4]Al content, and the [4]Al content is strongly ordered in the following way: T1B > T1A » T2B » T2A. The <M1-O>, <M2-O> and <M3–O> distances are linear functions of the mean ionic radius of their constituent cations. End-member compositions may be written as follows: A☐Mg2Mg5Si8O22(OH)2O22(OH)2; A☐Mg2(Mg3Al2)(Si6Al2)O22(OH)2; ANaMg2Mg5(Si7Al) These compositions define a plane in xyz space across which the data of Schindler et al. (2008), measured on amphiboles from amphibolites, follow a tightly constrained trajectory. Anthophyllite–gedrite amphiboles equilibrated under significantly different P-T conditions (e.g. igneous rocks, contact-metamorphic rocks) follow trends that diverge from this trajectory, with greater Na and [4]Al contents and relatively smaller [6]Al contents. Detailed examination of the local bond topology involving the A and M2 sites indicates that the maximum degree of bond-valence compensation will occur for incorporation of ANa and M2Al in the ratio 4:10, and hence 2.5 ANa = M2Al in these amphiboles. This relation closely fits the data of Schindler et al. (2008), suggesting that the variation in chemical composition in anthophyllite–gedrite amphiboles is strongly constrained by the anion bond-valence requirements of the Pnma amphibole structure. We further suggest that different compositional trends for ortho-amphiboles equilibrated under different P-T conditions are the result of the valence-sum rule operating with (different) bond-lengths characteristic of these P-T conditions.

The structure of prehnite Ca2Al(AlSi3O10)(OH)2, including H positions, has been determined by a combination of single-crystal X-ray diffraction and neutron powder diffraction on four natural samples. The symmetry of the average structure with Al/Si disordered at the T2 siteis Pncm. However, for four of the crystals studied, numerous violations of the n- and c-glide reflection conditions indicate lower symmetry corresponding to space groups P2cm and P2/n and Al-Si ordered structures, possibly as domains of different symmetries and ordering within a single crystal. Time-of-flight neutron powder diffraction was carried out on a sample from Mali at 293 K and 2 K. The structure was refined in space group Pncm by Rietveld analysis. Although it was not possible to locate the missing H using the 293 K neutron data, these data were used to refine the H position located approximately by single-crystal XRD and to refine Uiso. For the 2 K neutron powder diffraction data, H was located directly by difference-Fourier synthesis and its refined position found to be in close agreement with that obtained by the combined XRD/neutron 293 K dataset.

Calcium carbonate biominerals are frequently analysed in materials science due to their abundance, diversity and unique material properties. Aragonite nacre is intensively studied, but less information is available about the material properties of biogenic calcite, despite its occurrence in a wide range of structures in different organisms. In particular, there is insufficient knowledge about how preferential crystallographic orientations influence these material properties. Here, we study the influence of crystallography on material properties in calcite semi-nacre and fibres of brachiopod shells using nanoindentation and electron backscatter diffraction (EBSD). The nano-indentation results show that calcite semi-nacre is a harder and stiffer (H ≈ 3—5 GPa; E = 50–85 GPa) biomineral structure than calcite fibres (H = 0.4—3 GPa; E = 30—60 GPa). The integration of EBSD to these studies has revealed a relationship between the crystallography and material properties at high spatial resolution for calcite semi-nacre. The presence of crystals with the c-axis perpendicular to the plane-of-view in longitudinal section increases hardness and stiffness. The present study determines how nano-indentation and EBSD can be combined to provide a detailed understanding of biomineral structures and their analysis for application in materials science.

We live at the dynamic interface between the solid Earth and its outer fluid envelopes. This interface, extending from the outer vegetation canopy to the base of active groundwater, was recently named the Critical Zone because it supports life and is increasingly impacted by human actions. Understanding the complex interactions between processes that operate in and shape the Critical Zone requires interdisciplinary approaches that span wide spatial and temporal scales. Tectonic processes, weathering, fluid transport, and biological processes control the function and structure of the Critical Zone. Three Critical Zone Observatories recently established by the U.S. National Science Foundation are designed to integrate studies of process interactions up to the watershed scale. A goal of the program is to build the three independently conceived observatories into a network from which broader understanding — larger spatial scales but also deeper insight — can emerge.

A suite of experimentally deformed single-crystal pyrite samples has been investigated using electron backscatter diffraction (EBSD). Single crystals were loaded parallel to <100> or <110> and deformed at a strain rate of 10-5 s-1, confining pressure of 300 MPa and temperatures of 600°C and 700°C. Although geometrically (Schmid factor) the {001}<100> slip system should not be activated in <100> loaded samples, lattice rotation and boundary trace analyses of the distorted crystals indicate this slip system is easier to justify. Determination of 75 MPa as the critical resolved shear stress (CRSS) for {001}<100> activation, in the <110> loaded crystals, suggests a crystal misalignment of ~5—15° in the <100> loaded crystals would be sufficient to activate the {001}<100> slip system. Therefore, {001}<100> is considered the dominant slip system in all of the single-crystal pyrite samples studied. Slip-system analysis of the experimentally deformed polycrystalline pyrite aggregates is consistent with the single-crystal findings, with the exception that {001}<11̄> also appears to be important, although less common than the {001}<100> slip system. The lack of crystal preferred orientation (CPO) development in the polycrystalline pyrite aggregates can be accounted for by the presence of two independent symmetrically equivalent slip systems more than satisfying the von Mises criterion.

Tourmaline from the Kat Chay mine, Momeik, near Mogok, Shan state, Myanmar, shows a variety of habits that resemble mushrooms, and it is commonly referred to as ‘mushroom tourmaline'. The structure of nine single crystals of elbaite, ranging in colour from pink to white to black and purple, extracted from two samples of mushroom tourmaline from Mogok, have been refined (SREF) to R indices of ~2.5% using graphite-monochromated Mo-Kα X-radiation. 11B and 27Al Magic Angle Spinning Nuclear Magnetic Resonance spectroscopy shows the presence of [4]B and the absence of [4]Al in samples with transition-metal content low enough to prevent paramagnetic quenching of the signal. Site populations were assigned from refined site-scattering values and unit formulae derived from electron-microprobe analyses of the crystals used for X-ray data collection. 57Fe Mössbauer spectroscopy shows that both Fe2+ and Fe3+ are present, and the site populations derived by structure refinement show that there is no Fe at the Z site; hence all Fe2+ and Fe3+ occurs at the Y site. The 57Fe Mössbauer spectra also show peaks due to intervalence charge-transfer involving Fe2+ and Fe3+ at adjacent Y sites. Calculation of the probability of the total amount of Fe occurring as Fe2+–Fe3+ pairs for a random short-range distribution is in close accord with the observed amount of Fe involved in Fe2+–Fe3+, indicating that there is no short-range order involving Fe2+ and Fe3+ in these tourmalines.

A Visual Basic program (TOURCOMP) has been written to recast the tourmaline composition into end-member components from electron microprobe data or more complete tourmaline analyses. TOURCOMP is a program based on a linear algebraic model that directly calculates the end-member proportions of tourmalines from their structural formulae. The program is developed for IBM-compatible personal computers running under the Windows™ operating system. The source code has been also translated and compiled in order to run on an Apple computer. Analytical problems, uncertainties concerning site occupancies, and the normalization procedure to determine the structural formula are the main error sources. However, the method of recalculating tourmaline end-members presented in this paper is considered to provide reasonably good results, bearing in mind the chemical complexity of tourmaline.

The crystal structure of mosandrite, ideally Na2Ca4REETi(Si2O7)2OF3, a = 7.4184(8), b = 5.6789(6), c = 18.873(2) Å, β = 101.410(2)°, V = 779.35(5) Å3, space group P21/c, Z = 2, Dcalc = 3.363 g.cm-3, from the type locality, Låven (Skådön), Langesundsfjorden, Larvik, Vestfold, Norway, has been refined to Ri = 6.33% on the basis of 1113 unique reflections F°≥4σF. Electron microprobe analysis gave the empirical formula Na1.99(Ca3.93Sr0.02)Σ3.95(Ce0.41La0.16Nd0.13Pr0.04Sm0.02Dy0.01Y0.13)Σ0.90 (Ti0.864+Nb0.08Zr0.05)Σ0.99(Si207)2(F1.20O0.80)Σ2.00F2, Z = 2, calculated on the basis of 18 (O + F) a.p.f.u.. The crystal structure of mosandrite is a framework of TS (titanium silicate) blocks. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral). The TS block in mosandrite exhibits linkage and stereochemistry typical for Group I (Ti = 1 a.p.f.u.) Ti-disilicate minerals: two H sheets connect to the O sheet such that two (Si2O7) groups link to the trans edges of a Na polyhedron of the O sheet. The O sheet cations give Na(NaCa)Ti (4 a.p.f.u.). The TS blocks link via common vertices of (Si2O7) groups and common vertices and edges of Ca-dominant MH and Ap polyhedra. Two adjacent TS blocks are related by the glide plane cy. Composition and topology of the TS block in mosandrite and rinkite are identical. The crystal structure of mosandrite from the type locality is topologically and chemically identical to that of rinkite from the type locality of Kangerdluarssuk, Greenland.

Living systems exert exquisite control on all aspects of biomineral production and organic components, including proteins, are essential to this biological control. The protein-rich extrapallial (EP) fluid of bivalve molluscs is a strong candidate for the source of such proteins. Differences in calcium carbonate polymorphs between Modiolus modiolus and Mytilus edulis are concurrent with differences in EP fluid protein profiles. In conjunction with this biological control is the environmental influence which is interpreted using proxies such as δ18O to determine the history of ambient seawater temperature. In the horse mussel, Modiolus modiolus, the difference in oxygen isotope fractionation in the nacreous aragonite and the prismatic aragonite layer results in respective δ18O values of 2.1±0.2% and 2.5±0.2%. These δ18O values result in estimates of ambient seawater of 12.1±0.6°C and 10.2±0.6°C for nacreous and prismatic aragonite, respectively. Electron backscatter diffraction is used here to determine the crystallographic orientation at high spatial resolution, allowing the measurements of stable isotopes to be accurately mapped in terms of shell architecture. These preliminary data suggest that it is essential to account for both polymorph and crystal habit when deciphering ambient seawater temperature using δ18O as a proxy.

This work relates the crystal chemistry and the magnetic behaviour of a trioctahedral mica (chemical formula: (K0.90Na0.01Ca0.01Ba0.01 ☐0.07)(Al0.05Fe2+1.10Mg1.38Ti0.32Mn0.01☐0.04)(Al1.12Si2.88)O10 (F0.27OH1.27O0.46); unit cell parameters: a = 5.345(2) Å, b = 9.261(4) Å, c = 20.189(8) Å; β = 95.075(8)°) from Minto Block (Ungava peninsula, northern Quebec, Canada), a region characterized by high magnetic anomalies. Crystallographic and X-ray absorption spectroscopy data suggest a prevalent divalent oxidation state for Fe and a disordered Fe 2+ distribution in the two octahedral sites Ml and M2. The real part of magnetic susceptibility shows two peaks at ∼5.2 K and 120 K. However, as demonstrated by AC magnetic susceptibility measurements, the origin of the two effects is different: the peak position of the first one (i.e. the effect revealed at 5.2 K) is frequency-dependent, thus suggesting a spin-glass like behaviour. The effect at 120 K can instead be attributed to the occurrence of diluted phases in mica matrix, such as Fe oxides.