Mg-Mn amphibole (tirodite), with or without pyroxmangite in the total absence of pyroxenes and high-calcic pyroxenoids, occurs in the Mn silicate rocks of the Sausar Group, India. The rocks were metamorphosed to amphibolite facies condition (T ∼ 650°C, P ∼ 6 kbar). Tirodite-pyroxmangite pairs developed in both carbonate-free and rhodochrosite-bearing assemblages. Also tirodite coexists with either kutnahorite or manganoan calcite in the absence of pyroxmangite. Mineral reactions inferred from modal abundances and compositions of the phases indicate stabilization of the amphibole alone from a bivalent cation-bearing residual unbuffered XCO2 system with XMn < 0.3. On the other hand, tirodite-pyroxmangite pairs appeared in unbuffered low to intermediate XCO2 assemblages with XMn > 0.35. Pyroxenes and high-calcic pyroxenoids did not appear in the present situation, though they occur elsewhere in rocks with broadly similar contents of immobile components. Closely associated assemblages of diverse mineralogy suggest that the XMn and XCO2, rather than the physical conditions of metamorphism, are the decisive factors in promoting the observed phase assemblages.

Small, euhedral Mn-rich garnets (32–52 mol. % spessartine) from the Cairngorm granite, Eastern Grampian Highlands, Scotland, are considered to be of magmatic origin and have not been derived from the assimilation of metasedimentary material, despite their occurrence largely at the margins of the pluton. Similar garnets also occur in a late cross-cutting aplite sheet. The garnets in the granite crystallized early in the sequence and are thought to have formed in response to the ponding of Mn-rich fluids against the wall of the pluton. This Mn enrichment of the fluid phase continued throughout the evolution of the pluton, resulting in Mn-rich biotites and opaque oxides and the localized crystallization of Mn-rich garnets in aplite. Garnet contains up to 1.67 wt. % Y, but has not played a major role in the geochemical evolution of the Cairngorm granite, which has high SiO2 (72–77%) and is enriched in Y and HREE. Chemical analyses of garnets, biotites and rocks are given.

The crystal structure of gyrolite from Qarusait, Greenland, was solved and refined with the space group P and cell parameters a = 9.74(1), b = 9.74(1), c = 22.40(2)Å, α = 95.7(1)°, β = 91.5(1)°, γ = 120.0(1)°. The structure is built up by the stacking of the structural units already found in the crystal structure of reyerite (Merlino, 1972, 1988), namely tetrahedral sheets S1 and S2 and octahedral sheets O. The tetrahedral and octahedral sheets are connected by corner sharing to give rise to the complex layer which can be schematically described as 1OS2, where S2 and , as well as O and , are symmetry-related units. Successive complex layers with composition [Ca14Si23AlO60(OH)8]-5 are connected through an interlayer sheet made up by calcium and sodium cations and water molecules.

The unit cell content NaCa16Si23AlO60(OH)8·14H2O, determined by the structural study, was confirmed by a chemical analysis, apart from the indication of a somewhat larger water content. The crystal chemistry of gyrolite is discussed on the basis of the present structural results and the chemical data given in the literature for gyrolite from different localities: the crystal chemical formula which accounts for most gyrolite samples is Ca16Si24O60(OH)8·(14+x)H2O, with 0 ⩽ x ⩽ 3.

Stacking disorder, twinning and polytypic variants in gyrolite, as well as the structural relationships of gyrolite with truscottite, reyerite, fedorite and the synthetic phases K and Z are described and discussed.

Chromite inclusions in uvarovite-chrome garnet, chemically zoned chromite-chrome spinel and chrome spinel-olivine pairs from metacarbonates of the Oetztal-Stubai Complex (northern Tyrol, Austria) are described in terms of their textural occurrences and chemical compositions. Their genetic relationship in relation to the polymetamorphism of the region is discussed.

During a mineralogical study of guano-derived sedimentary phosphate ore from the Lamphun area of northwest Thailand, robertsite [Ca6(H2O)6Mn3+9O6(PO4)9.3H2O] was identified and concentrated to a level suitable for X-ray diffraction and chemical analysis. Robertsite has previously been described only in association with altered phosphatic pegmatites. This new occurrence in a phosphate deposit indicates that it may be found in a broad spectrum of sedimentary rocks.

A new cathodoluminescence-microscope has been developed with a considerably improved detection limit. Time-dependent luminescence intensity changes observed during electron bombardment enabled the recognition of short-lived, long-lived, and brown luminescence colour types in α-quartz.

Short-lived bottle-green or blue luminescence colours with zones of non-luminescing bands are very common in authigenic quartz overgrowths, fracture fillings or idiomorphic vein crystals. Dark brown, short-lived yellow or pink colours are often found in quartz replacing sulphate minerals. Quartz from tectonically active regions commonly exhibits a brown luminescence colour. A red luminescence colour is typical for quartz crystallized close to a volcanic dyke or sill.

The causes of these different and previously poorly understood luminescence colours were investigated using heat treatment, electron bombardment and electrodiffusion. Both natural and induced brown luminescence colours reflect the presence of lattice defects (nonbonding Si-O) due to twinning, mechanical deformation, particle bombardment or extremely rapid growth. The bottle-green and blue linearly polarized luminescence colour, characterized by a plane of polarization parallel to the c-axis, both depend on the presence of interstitial cations. The yellow and red luminescence colours in α-quartz both exhibit a plane of polarization perpendicular to the c-axis and appear to be related to the presence of trace elements in an oxidizing solution and to ferric iron respectively.

Isocubanite is a cubic polymorph of cubanite CuFe2S3, discovered in the submarine sulphide deposits of the East Pacific Rise (EPR) and the Red Sea, in association with chalcopyrite, pyrrhotine, pyrite, sphaterite or wurtzite and anhydrite. It was previously obtained artificially and mentioned as iss, ‘intermediate solid solution of CuFe2S3 composition’. Crystals are cubic with a = 5.303(3) Å and strongest lines in the X-ray powder pattern are 3.059 (10) 111, 1.876 (7) 220, 1.602 (5) 311. Euhedral grains range from a few microns up to 400 µm, with a Vickers microhardness of 175(25) kg/mm2 for P = 100 g. Isocubanite is usually intimately intergrown with iron- and zinc-rich chalcopyrite and is opaque with a metallic lustre and a bronze colour. Pinkish brown and isotropic in polished sections; reflectance values (SiC standard) are: 420 nm 22.73%, 460 nm 26.87, 500 nm 31.34, 540 nm 34.79, 580 nm 37.35, 620 nm 39.11,660 nm 40.32, 700 nm 41.33, 740 nm 41.91, 780 nm 42.50. Electron microprobe analyses gave (wt. %): Fe 41.64–42.49, Cu 20.79–21.52, Zn 0.77–1.09, S 35.49–35.82, corresponding to the formula (Cu,Zn)Fe2S3.

Isocubanite is characteristic of high-temperature (> 200 °C) present-day submarine sulphide deposits where hot hydrothermal fluids are quenched by seawater as in EPR deposits or by cooler brines as in Atlantis II Deep, in the Red Sea; it is unstable and therefore unusual in fossil ores. This cubic phase was previously observed and described more or less accurately as cubic cubanite, cubanite II, chalcopyrrhotite and iss; the name isocubanite, proposed in order to clarify the nomenclature, and this new description, were approved by the IMA Commission on New Minerals and Mineral Names.

Chevkinite/perrierite crystallized from a series of REE-enriched compositions, ranging from basalt through andesite to rhyolite at pressures from 7.5 to 20 kbar and temperatures from 900–1050°C. The Al2O3 content increased with increasing pressure, but no other consistent composition change was observed with pressure and temperature variation in this range. The REE partition pattern consistently favoured light over heavy REE, with a regular decrease in partition coefficients (D) from La through to Lu. D values increase with decreasing temperature and decreasing REE content (i.e. Henry's Law does not apply, as REE are essential structural constituents of chevkinite/perrierite), but appear unaffected by pressure and fo2. Chevkinite/perrierite may be a significant fractionating phase in evolving silicic magmas, or a residual phase from low degrees of partial melting of granulites. In both these circumstances it will exert a major control on the REE content of derivative liquids.

Pottsite occurs in the oxide zone of a tungsten mine northwest of Potts, Lander County, Nevada, and is named for the locality. It occurs with scheelite, clinobisvanite, bismutite, and vanadinite. The colour is yellow, luster adamantine. Dobs. is 7.0, Dcalc. 7.31. Uniax (-) ω = 2.49, ɛ = 2.37. Microprobe analysis gave PbO 32.4, Bi2O3 34.0, V2O5 26.6; H2O by Penfield method 6.71% (total 99.71%), leading to HPbBi(VO4)2·2H2O. Crystals are tetragonal 14122, a = 11.084, c = 12.634Å. Strongest powder diffraction lines are 4.618 (9), 4.168 (3), 3.210 (4), 3.062 (10), 2.476 (4), 2.252 (3).

Ecandrewsite, the zinc analogue of ilmenite, is a new mineral which was first described from the Broken Hill lode in 1970 and discovered subsequently in ores from Little Broken Hill (New South Wales) and the San Valentin Mine, Spain. The name ‘ecandrewsite’ was used in a partial description of the mineral in ‘Minerals of Broken Hill’ (1982), thereby establishing the Little Broken Hill locality, specifically the Melbourne Rockwell Mine, as the type locality. Microprobe analysis of ecandrewsite from the type locality gave ZnO 30.42 (wt.%), FeO (total Fe) 11.37, MnO 7.64, TiO2 50.12, total 99.6%, yielding an empirical formula of (Zn0.59Fe0.24Mn0.17)1.00Ti0.99O3 based on 3 oxygen atoms. All compositions from Little Broken Hill and the San Valentin Mine are ferroan manganoan ecandrewsite. The strongest lines in the X-ray powder diffraction data are (d in Å, (hkil), I/Io):2.746, (104), 100; 2.545, (110), 80; 1.867, (024), 40; 3.734, (012), 30; 1.470, (3030), 30; 1.723, (116), 25. Ecandrewsite is hexagonal, space group RR3¯ assigned from a structural study, with a = 5.090(1), c = 14.036(2)Å, V = 314.6(3)Å3, Z = 6, D(calc.) = 4.99. The mineral is opaque, dark brown to black with a similar streak, and a submetallic lustre. In plane polarized light the reflection colour is greyish white with a pinkish tinge. Reflection pleochroism is weak, but anisotropism is strong with colours from greenish grey to dark brownish grey. Reflectance data in air between 470 and 650 nm are given. At the type locality, ecandrewsite forms disseminated tabular euhedral grains up to 250 × 50 µm, in quartz-rich metasediments. Associated minerals include almandine-spessartine, ferroan gahnite and rutile. The name is for E. C. Andrews, pioneering geologist in the Broken Hill region of New South Wales. Type material consisting of one grain is preserved in the Museum of Victoria (M35700). The mineral and name were approved by the IMA Commission on New Minerals and Mineral Names in 1979.

Intracellular crystals of aragonite have been identified by selected area electron diffraction (SAED) in the freshwater filamentous alga Spirogyra sp. which grows sporadically as carpets in the Thames river, Ontario, Canada. The crystals are 2 to 24 µm in length, and characterized by a unique cross-shaped morphology, in which needle-like, or prismatic outgrowths develop from a common axis. Crystals may be dispersed through filaments, but tend to cluster as aggregates towards the centre.

Solution studies have been carried out on natural and synthetic arsenate minerals, which are often found in the oxide zones of base metal orebodies. Solubility products and free energy of formation data have been derived for the minerals olivenite, cornubite, clinoclase, adamite, legrandite, euchroite, duftite, conichalcite, austinite, bayldonite, and schultenite at 298.2 K (25 °C). The data have been used in turn to construct stability field diagrams illustrating the chemical conditions under which the various species may crystallize from aqueous solution. This equilibrium model is then compared with several natural occurrences of the arsenate suites and it is demonstrated that it can be used to explain a number of observed paragenetic sequences. Descriptions of solution conditions which describe the stabilities of the arsenate minerals with respect to more commonly found secondary minerals of Pb(II), Cu(II), and Zn(II) involve more complex calculations and estimates of the likely levels of various dissolved species, but it is shown how these may be taken into account in the development of a more complex equilibrium model.

Sieleckiite is a new copper aluminium phosphate discovered at the Mt Oxide Copper Mine, 150 km north of Mt Isa, Queensland, Australia. It occurs with variscite, turquoise, libethenite and minor pseudomalachite in a fracture in a boulder of quartzite and shale. Sieleckiite forms deep sky blue to royal blue spheres up to 0.5 mm in diameter, made up of fibrous radiating crystals between 20 and 100 µm long and 1 to 2 µm wide. The mineral has a very pale blue streak and a pearly lustre on uneven fracture surfaces. Hardness is about 3 and the measured density is 3.02 g cm−3. The average of nine electron microprobe analyses gave CuO 32.39, Al2O3 26.57, P2O5 19.42%. Separate analyses gave H2O 18.1, CO2 1.6% (carbonate impurity). These data gave an empirical formula of Cu3.1Al4.0(PO4)2.1(OH)12.1.7H2O, calculated on the basis of 22 oxygen atoms. The simplified formula is Cu3Al4.0(PO4)2.1(OH)12.2H2O. The strongest lines in the X-ray powder diffraction pattern are {d(I)(hkl)}; 9.12(50)(100), 5.06(100)(101), 3.852(100)(111), 3.276(30)(2¯20), 2.827(50)(1¯02,102), 2.460(50)(3¯21). These data were indexed on a triclinic cell with a 9.41(8), b 7.56(5), c 5.95(6) Å, α 90.25(12)° β 91.27(12)° γ 104.02(7)° and a volume of 410.8(5) Å3. For Z = 1, the calculated density is 2.94 g cm−3. Optical properties could not be determined in full; the refractive indices are between 1.63 and 1.66, pleochroism is very weak from colourless to very pale blue.

The mineral is named for the discoverer, Robert Sielecki (1958- ). Type specimens are preserved at the Museum of Victoria and the South Australian Museum. Sieleckiite was approved by the IMA Commission on New Minerals and Mineral Names prior to publication.

The crystal structure of reyerite, (Na,K)2Ca14Si22Al2O58(OH)8.6H2O, Z = 1, was refined in the space group P, a = 9.765, c = 19.067Å, to R = 0.064 for 1540 reflections. The structure is composed of the following structural units: (a) tetrahedral sheets S1, with composition (Si8O20)8−, characterized by six-membered rings of tetrahedra; (b) tetrahedral sheets S2, characterized by six-membered rings of tetrahedra, with six tetrahedra pointing in one direction and two pointing in the other direction—the apical oxygens of these two tetrahedra connect two inversion-related S2 sheets to build double sheets, with composition (Si14Al2O38)14− and ordered distribution of aluminum cations; (c) sheets O of edge-sharing calcium octahedra. The various structural units are connected through corner sharing according to the schematic sequence ……; the corresponding composition is [Ca14Si22Al2O58(OH)8]2−. The charge balance is restored by alkali cations which are placed, together with water molecules, in the cavities of the structure at the level of the double tetrahedral sheet.

Criddleite, ideally TlAg2Au3Sb10S10, is a rare constituent within the Hemlo gold deposit, Hemlo, Ontario, Canada. The mineral occurs as 20 to 50 µm-sized lath-like, tabular or anhedral grains usually surrounding or penetrating aurostibite, or associated with native antimony, native gold and stibnite. Criddleite is opaque with a metallic lustre and a black streak. It has been synthesized by reacting TlSbS2 and high purity Ag, Au, Sb and S in an evacuated silica glass tube at 400 °C. The measured density of the synthetic material is 6.86; the calculated density is 6.57 g/cm3. The difference is due to minor admixed aurostibite, native antimony and a dyscrasite-like phase within the charge. VHN25 is 94–129. Mohs hardness (calc.) = 3–3 ½. In reflected plane-polarized light in air, natural criddleite is weakly bireflectant with a discernible reflectance pleochroism from grey-blue to slightly greenish grey-blue. The mineral has a distinct to moderate anisotropy with rotation tints in shades of buff to slate grey. Reflectance spectra and colour values for both natural and synthetic criddleite are given. X-ray study showed that synthetic criddleite is monoclinic (pseudotetragonal) with refined unit-cell parameters a = 20.015(2), b = 8.075(2), c = 7.831(2) Å, β = 92.01(2)°, V = 1264.9 ± 1.0 Å3 and a:b:c = 2.4786: 1:0.9698. The space group choices are A2/m(12), A2(5) or Am(8), diffraction aspect A*/*. The seven strongest lines in the X-ray powder diffraction pattern [d in Å (I) (hkl)] are: 5.63(90) (011), 3.91(50) (002), 3.456(50) (320), 2.860(70) (700), 2.813(100) (022), 2.018(60) (040) and 1.959(70) (004). Electron microprobe analyses are reported of natural criddleite in five polished sections of drill core from four holes. The averaged empirical formulae, based on 26 atoms, are Tl0.92Ag1.99Au2.93Sb9.87S10.28 (natural) and Tl0.94Ag2.03Au2.89Sb9.76S10.38 (synthetic).

Small stones were recovered from a meteorite shower observed in Cameroon on November 13, 1952. The majority are LL6 specimens, Galim (a), but one is a chondrule-rich enstatite chondrite, Galim (b). Petrology and mineral chemistry were determined on polished sections of both types. Galim (a) has undergone multiple brecciation. During the first, chromite apparently recrystallized in healed fractures under more reducing conditions than those which prevailed when the silicates recrystallized. Galim (b) shows some features of petrologic type 3 but differs considerably from the other unequilibrated E chondrites. It is suggested that Galim (a) and Galim (b) belong to the same meteorite shower.