The manganese ores of Elba, South-eastern Desert, occur as numerous veins located within a narrow belt trending N.W.-S.E. Three ore-types were distinguished: hard crystalline ore consisting mainly of pyrolusite or ramsdellite or both, banded colloform ore consisting mainly of psilomelane, and in places cryptomelane, and soft nodular ore consisting of todorokite with minor amounts of psilomelane (or cryptomelane), nsutite, and pyrolusite. Black calcite and baryte occur in some of the veins and increase with depth.

Based on the field and mineralogical evidence the origin of the ore is discussed. It is suggested that the ore is a very low-temperature epithermal fissure deposit of black calcite type that occurs near the surface (oxidation zone) in brecciated zones along faults.

Biphosphammite, NH4H2PO4, recorded once as secondary powder in 1870, occurs with bat guano in Murra-el-elevyn cave, 31° 20′ S., 126° 0′ E., Western Australia.

The mineral occurs as tapering tetragonal prisms with pyramidal terminations, which are colourless to light buff, very soft, water soluble, contain fine syngenite inclusions, and have D 2·04, ω 1·525, ε 1·480 Space group. , a 7·4935 Å, c 7·340 Å, six strongest powder X-ray lines 3·75 Å (10) 200; 5·24 Å (9) 101; 3·02 Å (9) 112; 1·993 Å (8) 312,213; 2·65 Å (7) 220; 2·368 Å (7) 310,301. Partial analysis of purest available material gave: P2O5 51·1, K2O 14·2, (NH4)2O 12·3, SO2 5·59, Na2O 0·16, water-insolubles 0·81 per cent, remainder mainly CaO and H2O. Calculated mineral content is 88 % biphosphammite (62 % NH4H2PO4, 38% isomorphous KH2PO4), 11·5% syngenite, insolubles 0·81 % calc. total 100·3 per cent.

Material proposed to be neotype is preserved at the Government Chemical Laboratories, Perth, Western Australia.

Cobalt-rich spinel is found as a ∼200 µm inclusion, together with a glassy phase, in a gem-quality blue sapphire from Bo Ploi, Thailand. This is the first reported natural occurrence of such a spinel. Its composition is directly analogous with that of cochromite, a previously reported rare cobalt-rich chromite. The compositional ranges for the cobalt-rich spinel, obtained using electron microprobe and proton microprobe (methods described below), are Al2O3 48.18–61.27 %, CoO 19.7–22.84 %, Cr2O3 0–12.28 %, FeO 8.64–9.67 %, MgO 6.04–6.89, TiO2 0.49–0.73 %, Ni 2251–2532 p.p.m., Zn 335–371 p.p.m., Mn < 177–849 p.p.m., Ga 113–153 p.p.m., Nb 24–1252 p.p.m., Zr <4–167 p.p.m., Sn 22–428 p.p.m., As <4–56 p.p.m., Sr <4–59 p.p.m., Ag 13–64 p.p.m. Transition elements decrease in abundance from core to rim of the spinel while the other elements increase. Crystal chemical considerations suggest that a vacancy-creating substitution mechanism may be operative in the cobalt-rich spinel despite the small scale, i.e. 3Co2+ = 2Al3+ + [4]□. The glassy phase coexisting with the spinel is likely to be the product of heating by the host basaltic magma. The mode of occurrence of the cobalt-rich spinel prevents further physical investigation. This unusual spinel is considered to be the result of a complex magma mixing process in the lower crust.

Four size fractions have been separated and studied in eight samples of Cambrian greywackes, ranging from non-metamorphic to low metamorphic grade. Chemical study included analyses of each size fraction and comparison with the whole rock analysis. Mineralogical study involved analyses of individual crystals using microprobe (> 6 µm) and STEM (< 6 µm). This showed that in each fraction, a progressive homogenization of the mineralogical composition occurred during the development of metamorphism; that chemical transfers especially of Fe-Mg and K-Na, occurred between fine and coarse fractions and that recrystallization in fine and coarse fractions was simultaneous.

A horizon containing graphite in the Early Silurian slates of the Eastern Central System, Central Spain, has been studied. The carbonaceous slates contain quartz, muscovite, graphitized organic matter, plagioclase, pyrite and apatite; and the slates above the graphite horizon contain quartz, phengite, plagioclase and chlorite. The origin of the graphite is related to a period of very slow accumulation rate, anoxic seafloors deep-water upwellings and plankton blooms. The chlorite and graphite are mutually exclusive and by' using the chlori te AlIV content and the graphite Co parameter, the conditions of metamorphism were calculated to be 300 ± 20°C and 1.5-2 kbar.

Lead-zinc ore-bodies in dolomite at Broken Hill, Northern Rhodesia, consist of a sulphide core surrounded by an oxidized sheath. Oxidation has been proved to persist to a depth of at least 1150 ft. below surface. In the transitional zone between sulphide and oxidized ore galena forms a thin rim to relict masses of blende, and farther into the sulphide core it penetrates the blende along cracks and cleavages. Locally it comprises over 5 % of the ore. From its relations to smithsonite and willemite it is clearly supergene in origin and must have been deposited above the water table. This considerable migration of lead in the zone of weathering is believed to have occurred during a former period of aridity.

Pyrophanite is widely distributed in metamorphic Mn-rich rock assemblages of the Gangpur Group, India. It occurs in two distinct habits: as an independent phase, and as an exsolved phase within hematite. The well developed large sized crystals coexist with spessartine in Mn-silicate facies rocks. In contrast, the exsolved crystals occur as fine needle/bleb-like crystallites intergrown with hematite in Mn-silicate-oxide facies rocks. Compositionally the exsolved crystals are enriched in iron, present in both the ferric and ferrous states. The two morphologies of pyrophanite attest to their formation under different environmental conditions. The independent pyrophanite is formed from a Mn-Ti rich precursor under low oxygen fugacity conditions while the hematite-pyrophanite intergrowth evolved from an Fe-Mn-Ti rich precursor under higher fO2 conditions.

Contact metamorphism in the aureole of the Easky adamellite produced andalusite at the expense of regional staurolite, kyanite, and garnet. In the inner aureole sillimanite and K-feldspar also grew. Cordierite is only rarely present. Conditions of metamorphism in the inner aureole have been deduced from five independent criteria as 595 ± 30 °C and 2.5 ± 0.5kb. The nearby Lough Talt adamellite was emplaced at slightly higher pressures. Some aureole rocks have undergone oxidation with conversion of regional garnet to magnetite and andalusite. The reacting assemblage buffered ƒO2 near 10−17 bars. It is inferred that oxidation was caused by movement of H2O from the country rocks into the intrusion.

Infrared spectroscopy is a rapid method of distinguishing between pseudomalachite and its polymorphs reichenbachite and ludjibaite. This technique, backed by X-ray diffraction has shown that a number of specimens labelled ‘pseudomalachite’ from Cornwall, in particular from Old Gunnislake mine, are of reichenbachite, thus identified for the first time from the British Isles. Reichenbachite has also been identified with pseudomalachite from Miguel Vacas mine, Vila Viçosa, Evora, Portugal. Identification of pseudomalachite from a number of other localities world-wide has been confirmed, and some specimens have been shown to be arsenatian.

The ammonium content of pegmatites, aplites and granites from Alijó-Sanfins, northern Portugal, averages 162, 109 and 159 ppm respectively. There is no systematic difference in the NH4/K ratio between these rocks, and the variation in their ammonium content is mainly due to variations in the amount of potassium minerals they contain. The K-feldspars have higher NH4+ contents than the muscovites, but lower NH4/K ratios. The preference of NH4+ for micas rather than feldspars is not as great as that shown by rubidium. The ammonium content of pegmatites in general is highly variable, and is largely determined by the nature of the granites with which they are associated.

A reinvestigation of uranospathite from the type locality, Redruth, Cornwall, shows that it is an aluminium uranyl phosphate belonging to the torbernite series but more highly hydrated than other members thereof. The composition (HAl)0·5(UO2)2(PO4)2.20H2O was derived by indirect methods and by making use of analysis by the electron microprobe, which showed an Al2O3 content 2·6% in the partially dehydrated state. Unit-cell dimensions: a 7·00, c 30·02 Å, Z = 2. Probable space group P42/n. Strongest lines of the powder pattern: 15·22 (10) 002, 7·60 (10) 004, 4·93 (10) 110, 111, 3·50 (8) 116, 200, 201.

The mineral is unstable and unless preserved at low temperature or in a humid atmosphere converts into a new phase with a loss of 10- 12H2O. This phase (HAl)0.5 (UO2)2(PO4)2.8–10H2O is identical with the mineral sabugalite. Experimental work led to the synthesis of a hydrate with the composition (HAl)o·5(UO2)2(PO4)2. 16H2O, but not to fully hydrated uranospathite. This synthetic compound also dehydrates rapidly under normal conditions, converting into the same phase as does natural uranospathite. Arsenian uranospathite occurs at Menzenschwand in the Southern Black Forest.

Arsenuranospathite proper is a new mineral found at Menzenschwand and also at Wittichen in the Central Black Forest. It forms lathlike or wedge-shaped crystals of orthorhombic symmetry. Forms: {100}, {010}, {110}, {001}. Cleavage {001} perfect, {100} and {010} good. Hardness probably about 2, ρcak2·54 g cm −3. White to pale yellow. Streak white. Fluoresces greenish in ultra-violet light with variable intensity.

The single-crystal X-ray structure of tungstenian wulfenite-I41/a containing 10 mol.% WO3 from the San Francisco mine, Sonora, Mexico, space group I41/a, a = 5.436(2), c = 12.068(8)Å and Z = 4, has been refined to R = 0.052. The Mo and W are disordered over special position 4a (0,0,0) in the lattice. Tungstenian wulfenite-I4̄ (‘chillagite’) from the Christmas Gift mine, Chillagoe, Queensland, Australia (Museum of Victoria specimen M16934), crystallizes in the closely related tetragonal space group I4̄, with a = 5.441(1), c = 12.068(6) Å and Z = 4. The structure was refined to R = 0.038. Refined site occupancy factors show that Mo and W are not distributed equally over the two crystallographically independent Mo/W positions, being 0.136(2) for Mo and 0.114(2) for W in special position 2a (0,0,0) and 0.184(2) for Mo and 0.066(2) for W in special position 2c (0,Ý,Ü). These give a composition corresponding to wulfenite64stolzite36, in agreement with analytical data. The Mo/W distributions in the unit cell provide one explanation for the origin of hemihedrism in the wulfenite-stolzite series.

In vein material from the abandoned copper mine at Dhurode, County Cork, Republic of Ireland, the sulphosalt meneghinite is partly replaced by later minerals, notably a symplectite of galena and bournonite. Mineral analyses and proportions indicate that the bulk Pb/Sb ratio in the symplectite is almost identical to that of the meneghinite. It is inferred that Pb and Sb were the relatively immobile elements whose short-range segregation controlled the scale of symplectite intergrowth, during a diffusive replacement reaction in which Cu and S were added from the vein-forming fluid. This is the second sulphosalt-bearing symplectite for which immobile elements have been identified. In both cases, the inferred replacement reaction causes a volume increase, approximately 15% in the present example.

The Minastira granite, a c. 25 Ma subvolcanic plug of fine-grained granitic rock in the Cordillera Oriental of SE Peru, has preserved textures indicative of a history involving mixing of at least two magmas, a volumetrically dominant felsic component and a less voluminous mafic one. The felsic component is represented by variably fractured, altered and embayed crystals of quartz, feldspar, biotite with minor coarsegrained melt- and fluid-inclusion rich apatite, and possible cordierite (now a pseudomorphous Fe-Mg phase), whereas the mafic component is represented by calcic plagioclase. The process of magma mixing is reflected by: (1) ubiquitous sieved-textured plagioclase with complex textural relationships; (2) a large range in plagioclase compositions with reversals and spike patterns in profiles; (3) embayed and internally fractured (thermal shock?) quartz; (4) the rare occurrence of pyroxene coronas on quartz; and (5) textures within biotite suggestive of its incipient breakdown. The lack of mafic enclaves indicates that physico-chemical conditions of the mixing were conducive to homogenization (i.e. chemical diffusion) and a superficially homogeneous rock is now observed. The association of glomeroclasts of crystals originating from both the mafic and felsic end members and a quenched quartz-feldspar matrix indicate that the mixing occurred in an underlying magma chamber.

Yellow blades on joint surfaces in granite from Merrivale quarry, Dartmoor, Devon, are shown to be of a slightly aresenatian variety of phurcalite by X-ray powder diffraction, infrared spectroscopy, electron microprobe and thermal analyses and optical methods. The results from these techniques are tabulated, including assignments for infrared absorption bands. Comparison of X-ray powder diffraction, infrared spectroscopic and optical data with those obtained from samples of ‘nisaite’, an incompletely described mineral from Nisa, Portugal, indicates that the latter is also phurcalite.

Serpentinized ultramafic rocks recovered from beneath the southern Iberia Abyssal Plain (Ocean Drilling Programme Leg 173) provide the first record of fractal carbonate replacement patterns in a serpentinite. The patterns are expressed as microscopic branching aggregates (clusters) of aragonite disseminated throughout the serpentinites. Aragonite growth was the final mineralization event. The aragonite diminishes rapidly in quantity from an essential to a trace component of the serpentinite over a distance of ∼40 m from a normal fault. Decreasing abundance of aragonite away from the normal fault links the growth of the carbonate to the multistage hydrothermal mineralization associated with the fault.

Aragonite clusters are concentrated in picrolite, where they are interwoven with colloid-sized chrysotile, and show fractal growth habits. Areas adjacent to the clusters are sites of Mg enrichment of the serpentine medium relative to aragonite-free picrolite. It is interpreted that the aragonite clusters result from incursions of reactive seawater solutions through fine-scale pore structures in and around the fault in response to pressure gradients emanating from active tectonism. Cluster growth is interpreted to be a percolation phenomenon and provides a novel source of information on the nature of fine-scale reactive fluid flow, pore-space connectivity, and carbonate replacement processes in serpentinites.

Aguilarite, Ag4SeS, occurs in a hydrothermal vein deposit associated with sphalerite, chalcopyrite, galena, and native silver. Physical and chemical data agree with descriptions from Guanajuato (type locality). Differential thermal analysis of synthetic material indicates an inversion temperature of 122±1 °C. The mineral crystallized late in the paragenetic sequence, probably slightly above 200 °C.

Two different spinels, analyses of which are given, occur in the layered ultramafic rocks at Dawros. Chrome spinel occurs both as gravity-stratified cumulates and as complex orbs, while an Al-rich spinel is both in rocks of the main Dawros magmatic sequence and in an association with an aluminous bronzite, which may originate by recrystallization. It is concluded that while the chrome spinel is certainly of magmatic origin, the aluminous spinel is probably partly of magmatic and partly of recrystallization origin.