Found at the Joe and Grand Central mines, Tombstone, Arizona, USA, in quartz gangue with girdite, rodalquilarite, bromargyrite, and gold. Crystals orthorhombic, tabular to scaly on {010} up to 1 mm; H = 2, colour white, Dmeas = 4.98 ± 0.12.

Chemical analysis gave PbO 58.2 %, TeO3 28.6, SO3 6.8, H2O 4.7. Easily fusible to red-brown slag and soluble in cold, dilute acids.

Crystals orthorhombic Cmcm; a = 9.67 Å, h = 19.56, c = 10.47. Strongest lines 9.778 (10), 3.426 (6), 3.250 (6B), 3.560 (5B), 3.338 (5), 3.033 (5), 2.934 (5), 2.603 (5). Dcalc = 5.15, Z = 16. Indices are α = 1.897, β = 1.940, γ = 1.942, 2Va = 24°; γ‖a, α‖b, β‖c.

The mineral and name have been approved by the Commission on New Minerals and New Mineral Names, IMA.

Spectral ellipsometry in the range 240 nm to 540 nm has been used to investigate the influence of surface damage induced by mechanical polishing and surface films of CuO on the optical properties of pure synthetic cuprite. Comparison is made between bulk CuO and thin film CuO produced by low-temperature oxidation of cuprite. The effects of strain and disorder are discussed in relation to the suppression of excitonic transitions. Recently developed techniques have been used to simplify the analysis and take full advantage of the spectral data.

Within the Alston Orefield of the North Pennines, glaucodot and gersdorffite have been found in samples from Tynebottom Mine, Garrigill, and zoned gersdorffite has been found from Nenthead and the Great Sulphur Vein. At Scar Crag in the English Lake District, glaucodot and alloclase (the first reported occurrence in the United Kingdom) occur associated with arsenopyrite and minor cobaltite and skutterudite. The mineralogy and parageneses of these associations have been studied by ore microscopy, X-ray powder photography, and electron probe microanalysis.

Electron probe microanalysis shows a considerable range in nickel content in the sulpharsenides from the Alston Orefield with a relatively constant Co:Fe ratio. Samples from Scar Crag contain no nickel but exhibit almost a complete range of Co:Fe ratios from FeAsS to CoAsS. The compositions of the Alston Orefield sulpharsenides, in particular, show them to be metastable phases when compared with data from synthetic studies. At Tynebottom Mine, glaucodot and gersdorffite overgrow arsenical marcasite, and at Nenthead and the Great Sulphur Vein, early pyrite framboids or euhedra act as cores to zoned gersdorffite crystals. The Scar Crag sulpharsenides occur in a quartz chlorite apatite vein with the glaucodot and alloclase as overgrowths on arsenopyrite.

In the case of the Scar Crag association, consideration of the compositions of coexisting phases, together with precise determinations of the arsenic content of the arsenopyrites, has permitted speculation regarding temperatures and sulphur activities during ore formation. Estimated ranges are Tc. 400 °C–300 °C and aS2 ≈ 10−9–10−11 11 bar. The occurrence of the sulpharsenides in the Alston Orefield correlates with further geochemical differences compared to other Pennine ores, differences that have been linked to higher temperatures of formation and a magmatic contribution to the ore-forming fluid. The Scar Crag mineralization may be related to a postulated stock intrusion beneath Causey Pike and the geographical proximity of the Alston and Scar Crag occurrences does suggest the possibility of a genetic link.

The results of measurements of diffuse reflectance over the wavelength range 200 < λ < 2500 nm are reported for sphalerite, cinnabar, alabandite, chalcopyrite, bornite, orpiment, stibnite, bismuthinite, enargite, and pyrargyrite, and for eight pyrite-type and four NiAs-type compounds. Some spectral assignments have been made.

Optical properties are related to the absorption spectrum (and through this to composition and structure) in a rational way. Absolute reflectances tend to increase with mean atomic number (z) through the operation of the ‘z-sum rule’, and at constant z they decrease as the band gap increases. Bireflectance is structurally controlled, being weak in derivatives of the cubic sphalerite and pyrite structures, moderate in derivatives of wurtzite and NiAs, and strong in anisodesmic structures such as that of stibnite. Extreme bireflectance occurs in anisodesmic structures with strong dichroic absorption bands in the visible (molybdenite, covelline).

The dispersion of reflectance (dR/dλ) depends on the position of the centre of the main absorption envelope in relation to the visible spectrum. For λ > , dispersion is normal (Rblue > Rred, dR/dλ negative), the streak is light or coloured, and polished surfaces tend to be bluish. For λ < , dispersion is reversed (Rred > Rblue), the streak is dark, and polished surfaces are yellowish. Polished surfaces are white or grey if absorption varies little through the visible or strongly coloured if it varies rapidly (covelline, chalcopyrite).

An undeformed metadolerite dyke cutting foliated pyroxene-granulite facies gneisses in the Jotunhelm, Norway, has almandine rods replacing the cores of plagioclase laths, although garnet is generally absent from the enclosing gneisses, and is not present in reaction zones between peridotites and gneisses. Chemical analyses of the dyke and its garnet, plagioclase, and clinopyroxene are given. The presence of garnet in the dyke is attributed to the low mg ratio of the rock. The nature of the reaction leading to garnet pseudomorphous after plagioclase is discussed.

Previous interpretations relating to precipitation of anorthoclase megacrysts from alkaline basaltic magmas under high-pressure conditions are contradicted. It is proposed that these feldspars were crystallized above the solvus from hydrous melts at shallow depths, under low-pressure equilibrium conditions. These melts had been considerably enriched with volatiles of sodium, strontium, and barium, and to some extent also of rubidium.

A new analysis of the type material of cheralite specifies the individual rare earth elements. Unit cell contents are: (REE1.58Th1.15Ca1.03Pb0.05U0.15)3.96 (P3.67Si0.33)4.01O16. Refinement of the cell parameters based on new XRD data shows that a = 6.7515 ± 0,0005 Å, b = 6.9625 ± 0.0005, c = 6.468 ± 0.0005, β = 103° 53′, giving a cell volume of 295.2 Å3. Space group P21/n.

Electron-microscope observations of the oxidation products of olivine suggest that oxidation results in the formation ofplatelets of an ‘oxidized olivine’ phase, which has a superstructure of the olivine structure. Subsequently this intermediate phase breaks down by a cellular decomposition process to a eutectoidal intergrowth of magnetite and pyroxene. This intergrowth is responsible for the dendritic magnetite inclusions commonly observed in some olivines from Rhum.

The rare nickel telluride mineral melonite is identified from Jaduguda uranium ore, Singhbhum Shear Zone, Bihar, India. Its physical, optical, chemical, and paragenetic characteristics are described. The composition as obtained by EPMA is NiTe1.66Bi0.06 or approximately Ni3(Te,Bi)5. The association of melonite with molybenite in this ore deposit is unusual, since melonite is generally associated with tellurides of gold and silver. This is the first reported occurrence of melonite from India.

Bohdanowiczite was first described in 1967 but incomplete data prevented its acceptance as a new mineral at that time. Additional data on the same material now characterize bohdanowiczite as a new species with the formula:

3[(Ag0.98Cu0.02)0.97(Bi0.97Pb0.03)1.02(Se0.83S0.17)2.01]

The mineral occurs in intimate intergrowths with clausthalite and wittichenite in polymetallic mineralization at Kletno in Poland. In reflected light bohdanowiczite has a creamy-yellow colour and short polysynthetic twinning is frequently observed. Cell parameters indexed on a hexagonal lattice are a = 4.183±0.008 Å and c = 19.561± 0.016 Å. Pm1 is the most likely space group. The strongest lines of the powder pattern are 2.91(100), 2.03(30), 3.40(20), 6.54(20), 2.09(18), 3.26(18). The calculated density is 7.72 gm/cm3 and the VHN between 63 and 96 kg/mm2.

Electron diffraction and electron-microprobe investigations have revealed the presence of order in the monazite-huttonite series. Chemical analyses from the literature and electron-microprobe analyses in this study show that the monazite-huttonite series, REPO4-ThSiO4, is only continuous if the contribution of F, M2+, and OH to the charge balance is taken into account. The electron-diffraction study points to ordered domain structures in the series.

Extensive substitution of Ni for Zn in hydrozincite from the Parc Mine, North Wales, has been observed. This is the first time that a substantial concentration of another transition metal in this mineral has been reported. The average composition of the nickeloan hydrozincite is Zn4.63Ni0.37(CO3)2(OH)6. The relationship of this new variety to other secondary carbonate-containing nickel minerals is discussed, as is the possibility of substitution of other transition metal ions into the hydrozincite lattice.

The maghemitization process, by which magnetic minerals with spinel structure become progressively oxidized but remain single phase spinels, seems to be an important feature of submarine weathering. Whether the process takes place by the minerals acquiring oxygen from the sea-water or by the sea-water leaching out iron, the controlling process is the diffusion of Fe2+ in the spinel structure. Magnetic studies have suggested that during maghemitization the availability for oxidation of Fe2+ in the tetrahedral (A) sites of the spinel structure is much less than that in octahedral (B) sites. In this study the Fe2+-containing spinels FeAl2O4, FeCr2O4, FeGa2O4, and Fe2GeO4, in which Fe2+ is predominantly in either A or B sites were prepared, and the diffusion of Fe2+ was studied by (1) interdiffusion experiments with the Mg2+ counterparts and (2) oxidation experiments in air. Fe2GeO4 (Fe2+ in B sites) was found to be associated with a higher interdiffusion coefficient and lower activation energy than FeAl2O4 (75% Fe2+ in A sites). Oxidation/diffusion activation energies of 0.27 and 0.71 eV were assigned to Fe2+ in B and A sites respectively. The experiments thus provide support for the maghemitization model in which Fe2+ in B sites is preferentially oxidized.

Both new species are retrograde or mesogene minerals that occur in tactites at the Christmas mine, Gila County, Arizona (USA). Gilalite is green, H = 2, D = 2.82. Biaxial (—), 2V small, α = 1.560, β = γ = 1.635. No single crystals found; strongest lines at 13.49 Å, (10); 10.97 (5); 7.786 (5). Analysis gave CuO 36.2%, MgO 2.3, CaO 3.8, MnO 0.5, SiO2 41.5, H2O 14.6, close to Cu5Si6O17·7H2O.

Apachite is blue, H = 2, D = 2.80. Biaxial (—), 2V small, α = 1.610, β = γ = 1.650. No single crystals found. Strongest lines are 12.90 Å (10); 3.168 (7); 7.663 (5). Analysis gave CuO 43.6%, FeO 0.3, MgO 1.7, CaO 1.8, SiO2 40.8, H2O 13.8, close to Cu9Si10O29·11H2O.

Chrome spinels from seams in the Rhum layered intrusion, Inner Hebrides, generally contain very fine platelets of exsolved phases. Despite the low bulk Ti content (< 1%) of the spinel grains, analytical electron microscopy shows these platelets to be highly enriched in titanium. Electron diffraction indicates the presence of platelets of two different phases, one a magnesian ilmenite, the other a defect spinel intermediate phase. The platelets are the result of oxidation of the spinel at moderate (c. 600 °C) temperatures and their distribution suggests that oxygen fugacity gradients existed across some of the seams.

Specimens of layered baryte containing a range of pyrite forms, including framboids, framboidal aggregates, spherulites, polyhedra, and zoned euhedral crystals from Kempfield, New South Wales, Australia, have been examined by mineragraphy, X-ray diffraction (XRD), X-ray fluorescence (XRF), and electron-probe microanalysis (EPMA). These investigations showed that the pyrite occurred in two forms—an arsenical variety containing approximately 5% arsenic in solid solution within the pyrite and a non-arsenical variety. EPMA studies indicate that the framboids and the cores of the zoned euhedral crystals have similar levels of arsenic and a genetic relationship is deduced to exist between these forms.

A hygroscopic, soft, pink mineral was discovered in Sinjar town, west of Mosul city. Wet chemical and X-ray diffraction analyses proved that the mineral has a composition of calcium chloride dihydrate CaCl2·2H2O, which has not been known in nature before. It is therefore a new mineral, and is named sinjarite after its locality.

This study is devoted to fractures produced by natural and artificial shock processes in non-porous rocks consisting essentially of quartz and feldspar. Petrological and textural investigations were performed using optical and scanning electron microscopic techniques. A microfracturation index is adapted from Short (1966, 1968a, b) in order to compare the fracture densities in different materials shocked in different ways. In all cases, the density of fractures in quartz and feldspar increases with increasing pressure to about 200 kb. At higher pressure this trend is reversed. Fracturing is more intense in feldspar than in quartz. Plane shock waves produced in laboratory scale experiments induce more fracturing than natural shock waves. However, such an increase is no larger than the scatter among the data and the experimental technique used in the laboratory can be considered realistic in terms of fracturing. Finally the correlation between pressure and fracture density is too poor to be of use for quantitative pressure calibrations of naturally shocked materials.

There is no direct correlation between the density of fractures and the number of planar elements observed. There is a negative correlation between fracturing and formation of diaplectic glass, Diaplectic glasses are remarkably weakly fractured compared with shocked minerals. The abrupt change in the slope of the curve giving the dependency of the density of fractures with pressure corresponds to the pressure at which diaplectic glass is formed. From petrographic considerations it is deduced that fracturing occurs at the end of the shock sequence, on pressure release, while diaplectic glasses are forming or already formed. Hypotheses of mechanical and thermal fracturing are examined; both are plausible, but a thermal origin may be preferred. The mechanism of formation of diaplectic glass is discussed with respect to results and deductions obtained by the study of fracturing. Diaplectic glass could represent a decompressed highdensity glass resulting from a single state transformation of a mineral, at high pressure.

In clinopyroxene-melt systems the distribution of chromium and vanadium ions departs from the general pattern of element partition as a function of ionic radius. These departures may be explained by crystal-field effects. Melt structure and the nature of the coordination of cations in the melt also help to determine the pattern of distribution and the extent of the departures from regularity.