The carbonatites at Loe Shilman, near Khyber in NW Pakistan, fenitize their country rocks to form a metasomatic zone c.100 m wide of alternate dark blue (mafic) and pale grey (felsic) banded fenites which grade into unfenitized bedded slates and phyllites. The Na-amphiboles in the banded fenites form a complete solid solution series between magnesio-arfvedsonite and magnesio-riebeckite which coexist with varying proportions of aegirine, albite, and K-feldspar, with or without phlogopite or biotite.

The amphiboles show a gradual decrease in Na2O, K2O, Mg ratio [100Mg/(Mg + FeT + Mn)] and iron oxidation ratio, and an increase in total iron away from the carbonatite contact. The pleochroism correlates with the chemistry and distance from the carbonatite contact.

The Mg ratio decreases from 74 to 35 away from the carbonatite contact. The iron oxidation ratio [100Fe3+/ (Fe3+ + Fe2+)] decreases in the magnesio-arfvedsonite for the first 30 metres from the carbonatite contact, and then increases in the magnesio-riebeckite from 40 to 60 metres from the carbonatite contact. K relative to Na decreases away from the contact in the amphibole, and the decrease in K causes an increase in vacancy in the A site. The main variation in the chemistry in this solid solution series is due to (K,Na)A+(Mg,Fe2+)c ⇌ □ + (Fe3+)c substitution.

It is shown here that dyke rocks of type localities for ‘soda-minettes’ are not minettes (= lamprophyres dominated by phlogopite and K-rich feldspar). It has long been suggested that ‘soda-minette’ also be applied to otherwise normal minettes from elsewhere that carry modally variable amounts of groundmass aegirine and/or, more commonly, arfvedsonitic to riebeckitic amphibole. Despite the presence of sodic pyriboles, these rocks are poorer in Na2O then minettes lacking these phases. ‘Soda-minette’ is thus misleading and self-contradictory to the many petrologists to whom ‘soda-’ legitimately connotes that the rock in question either has K/Na < 1 and/or is rich in albitic feldspar. To eliminate this ambiguity it is recommended, with the approval of twenty-six other petrologists, that ‘soda-minette’ no longer be used as a rock name. As minettes with Na-pyribole(s) are markedly K-rich and most are both ultrapotassic and peralkaline, independent of the modal abundance of the Na-pyrobile, it is suggested that one of these three chemical characteristics be utilized adjectivally in naming these minettes.

A number of geochemical plots are suggested by means of which metamorphosed quartzofeldspathic sedimentary rocks (meta-sandstones, meta-arkoses, quartzites, etc.) can be distinguished from their metamorphosed igneous mineralogical analogues (metarhyolite, meta-granite, etc.). These plots are applied to an enigmatic, partly mylonitized, quartzofeldspathic series, the Delaney Dome Formation, which is involved in a major thrust zone. The formation is shown to be igneous and is probably a meta-rhyolite. The plots proposed should have general application in identifying the precursors of both high-grade and low-grade quartzofeldspathic rocks of unknown origin.

Amphibolites from the Grampian Moines of Scotland contain clinopyroxene-plagioclase symplectites and plagioclase-hornblende coronas around garnet. The clinopyroxene-plagioclase symplectites are interpreted as former omphacites. It is inferred that an eclogitic garne-tomphacite-quartz assemblage once existed, but has since undergone partial reaction to an amphibolite facies hornblende-plagioclase assemblage. An early high-pressure metamorphic event occurred in parts of the Moine.

The origin in rocks of the common iron sulphides, pyrrhotine, Fe1-xS and pyrite, FeS2 and their behaviour during geochemical processes is best considered using the simplified redox reaction: 2FeS ⇌ FeS2 + Fe2+ + 2e−.

Thus pyrrhotine is more reduced than pyrite and is the stable iron sulphide formed from magmas except where relatively high oxygen fugacities result from falling pressure or hydrothermal alteration. Pyrite, on the other hand, is the stable iron sulphide in even the most reduced sedimentary rocks where it usually forms during diagenesis through bacteriogenic reduction of sulphate; it is stable throughout the pressure/temperature range endured by normal sedimentary rocks. Pyrrhotine after pyrite or sulphate in metasediments of regional metamorphic origin results mainly from progressive reduction on metamorphism due to the presence of graphite-buffered fluids. Pyrrhotine and/or pyrite may be precipitated from hydrothermal solutions on epigenetic or syngenetic mineralization but pyrrhotine will only be preserved if protected from oxidation to pyrite or to more oxidized species. Exhalative pyrrhotine appears to have been more common in Precambrian times and/or in depositional environments destined to become regionally metamorphosed. FeS can be considered to be the soluble iron sulphide, rather than FeS2, in reduced aqueous systems although pyrite may precipitate from solution as a result of redox reactions. The relatively soluble nature of FeS explains the observed mobility of iron sulphides in all rock types.

Ultramafic xenoliths enclosed in Plio-Quaternary alkali basalts from Tallante near Cartagne (southern Spain) are composed mainly of spinel lherzolites which are probably upper mantle residues. In many xenoliths, the spinel lherzolite is cut by pyroxenite or gabbroic anorthosite veinlets generally 0.2–3 cm thick. The clinopyroxenite veinlets were formed by high-pressure crystal-liquid segregation from alkali basalt magmas formed earlier than the host basalts, whereas mantle metasomatism played a role in the genesis of gabbroic anorthosites. Close to the contact with the veinlets, the spinel lherzolites are enriched in Ca, Fe, and some incompatible elements including light REE due to the migration of a fluid from the veinlets into the surrounding lherzolites. The host alkali basalts were derived from a heterogeneous, incompatible element-enriched upper-mantle source probably similar in composition and nature to the composite xenoliths, but were formed in a garnet stability field.

The paper discusses the mineralogy of eruptives from the Nandewar Volcano, which range in composition from hawaiite and trachyandesite to comendite via tristanite and mafic and peralkaline trachyte. Olivine, Ca-rich pyroxene, and amphibole display marked decreases in 100 Mg/(Mg + Fe) ratios in the sequence trachyandesite to comendite, reflecting variation in host rock compositions. The presence of tscher-makitic subcalcic pyroxene and aluminous bronzite megacrysts in several trachyandesites indicates that these experienced intratelluric crystallization at elevated pressures (6–8 kbar). Some titanomagnetite and plagioclase phenocrysts in trachyandesites may also be moderate pressure cognate precipitates. Groundmass pyroxenes of some trachytes and comendites are strongly acmitic. The presence or absence of coexisting alkali amphiboles and aenigmatite appears to reflect stability over a relatively broad range of fO2 conditions. Aenigmatite rims on titanomagnetite and ilmenite microphenocrysts in several peralkaline eruptives provides support for a ‘no-oxide’ field in T-fO2 space. The Fe-Ti oxide compositional data indicate that magmas spanning the spectrum trachy-andesite-comendite crystallized under conditions of decreasing T and fO2 which broadly coincided with the FMQ synthetic buffer curve. However, a voluminous group of slightly older associated rhyolites appear to have crystallized under significantly more oxidizing conditions.

This paper presents the results of an experimental study of muscovite solid solutions in the system K2O-M2+O-Al2O3-SiO2-H2O-(HF), with M2+ = Mg2+ or Fe2+ in the temperature range 300-700°C under 2 kbar PH2O. Muscovite solid solutions can be described, in this system, as the result of two substitutions. One is the phengitic substitution (x), which preserves the pure dioctahedral character of the mica; the second is the biotitic substitution (y), which leads to trioctahedral micas and does not change the composition of the tetrahedral layer Si3Al. The general formula of muscovite in this system is K(Al2−x−2y∕3M2+x+y□1−y∕3)(Si3+xAl1−x)O10(OH,F)2. Both substitutions x and y are more extensive at lower temperatures. The extent of solid solution decreases drastically with increasing temperature.

For T > 600°C, the phengitic substitution (x) becomes negligible, but some biotitic substitution (y) persists. This unsymmetrical decrease of the solid solution of muscovite with increasing temperature is similar to that previously observed in phlogopite, the micas with a tetrahedral layer composition of Si3Al being the most stable. The behaviour of muscovite solid solutions in the ferrous system is qualitatively identical to that observed in the magnesian one, but the extent of solid solution is smaller than with Mg2+. Fluorine neither changes the size nor the shape of the solid solution fields but increases their stability by about 50°C.

A comparison of these experimental results with data on natural muscovites is presented. Most natural primary (magmatic) granitic muscovites lie very close to the muscovite end member, in agreement with their high-temperature origin. Low-temperature muscovites (300–400°C), typically muscovites from hydrothermally altered granitic rocks, can have high x and y values. The rate of the biotitic substitution y can reach 0.6, which corresponds to an octahedral occupancy of 2.2 atoms per formula unit (based on 11 oxygens), consistent with the experimental data.

A crystal of painite discovered in 1979 in a parcel of rough gem spinel from Burma represents the third known crystal of the species. This crystal is similar to the type crystal in most respects. Chemical analyses of both the new crystal and the type crystal confirmed the essential constituents reported by Moore and Araki (1976) and showed in addition the presence of trace amounts of Fe, Cr, V, Ti, Na, and Hf. Optical absorption spectra suggest that the red colour of painite is caused principally by Cr3+ and V3+.

Milarite was found in a cavity of a small pegmatitic segregation in association with albite, stilpnomelane and chabazite. Hexagonal, well-shaped crystals of milarite up to 4 mm in length are transparent, pale green in colour, and show bright green cathodoluminescence. The refractive indices are: ω = 1.535, ε = 1.534(Na). D = 2.55 g cm−3. The unit cell dimensions are: a 10.418(4), c 13.817(7) Å, V 1298.7 Å3. Anomalous biaxial sectors and birefringent optical patterns are visible in basal section. 2V varies from 34° in the {0001} sector to 64° in {101} sector. OAP azimuths are related to the external hexagonal symmetry of the crystals. Microprobe analyses of sections perpendicular and parallel to the c-axis revealed a uniform distribution of alkalis, mainly K2O, whereas CaO and Al2O3 contents are slightly higher in prismatic and pyramidal sectors than in the basal sector, but no systematic chemical zoning can be distinguished. The Al2O3 content decreases in the outer zone of the crystal studied due to Be-Al substitution. The average ‘anhydrous’ chemical formula of the Strzegom milarite is: (K0.98Na0.01)Ca1.93Mn0.02(Be2.16Al0.93)(Si12O30). Infra-red data indicate the presence of H2O molecules in the milarite. Internal growth structures of the crystals indicate rhythmic fluctuations of the growth rate resulting in an internal strain, inducing anomalous optical patterns. HRTEM study did not reveal any significant distortion of the milarite lattice.

Laphamite, ideally As2(Se,S)3, is monoclinic, P21/n, with a = 11.86(1), b = 9.756(9), c = 4.265(9) Å, β = 90.17°, V = 493.5 Å3, Z = 4, D (calc.) = 4.60, D (meas.) = 4.5(1) g/cm3. Microprobe analysis yielded: As 47.0, Se 43.7, S 8.7, sum = 99.4 wt. %. In plane polarized light in polished section at about 3200 K laphamite is moderately bireflectant from white to grey. Reflection pleochroism is absent but fiery red internal reflections are characteristic as are golden yellow reflections along scratches. Anisotropy is moderate with grey rotation tints, masked in some sections by internal reflections. Reflectance spectra in air and oil between 400 and 700 nm are given. Colour values for the CIE illiminant C in air are, for R1 followed by R2: Y% 29.0, 33.5, λd 480, 478; Pe% 9.1, 8.7. Laphamite forms dark red crystals, up to 5.0 mm, associated with orpiment, arsenolite, and an unnamed phase, NH4AlF4, in a burning coal waste-dump at Burnside, Northumberland County, Pennsylvania.

Obradovicite, ideal formula H4CuFe2(AsO4) (MoO4)5 · 12H2O, occurs as fine pea-green clusters on quartz from Chuquicamata, Chile. Obradovicite is orthorhombic, space group Pcnm; a = 15.046, b = 14.848, c = 11.056 Å, Z = 4. The strongest powder pattern lines are (d Å, I, hkl) 10.565(8)(110), 8.906(10)(101), 7.424(8)(020), 5.733(5)(211), 3.761(3)(400), 3.686(4)(032), 3.466(3)(411), 3.344(4)(420). It is biaxial positive with α = 1.790, β = 1.798, γ = 1.811, 2Vz = 81°, a = Z, b = X, c = Y, with strong dispersion and pale yellow pleochroism. Specific gravity is 3.55 (meas.) or 3.68 (calc.) and the Mohs hardness is 2½ with no obvious cleavage. Obradovicite is similar to betpakdalite and sodium-betpakdalite except that it contains essential Cu and K (K > Na).

Erlianite was found in the Harhada iron deposit along the Jining-Erlian railway, Inner Mongolia Autonomous Region, People's Republic of China. The occurrence formed at a high pressure and low temperature and the mineral occurs sparingly, mainly on fracture surfaces on which there is evidence of movement. It is associated with quartz, magnetite, siderite, albite, stilpnomelane, minnesotaite, deerite, etc.

Erlianite is black with a brownish streak, silky lustre and occur as fibres, flakes, and lath-like aggregates. The grain size is 1–2 cm. It is not fluorescent. H = 3.7, D = 3.11. Cleavages on {001} and {100} are perfect; orthorhombic Pmmn or Pm21n with a = 23.20, b = 9.20, c = 13.18, Å and Z = 1. Strongest lines are 11.5(100)(200, 101), 3.05(50)(223,130), 2.89(60)(603,800,231,621), 2.61(60) (523,105,332,224), 2.52(50)(901,115,033,531), and 1.560(50) (12.0.5,14.2.0). Biaxial negative with α = 1.667, β = 1.674, γ = 1.679, 2V = 56–59°. Analysis gave SiO2 38.80, FeO 26.67, Fe2O3 21.26, V2O5 1.15, MgO 1.00, CaO 0.83, MnO 0.55, P2O5 0.051, K2O 0.079, Na2O 0.09, Al2O3 0.19, TiO2 0.38, H2O+ 7.65, H2O- 0.90, total 99.60%, leading to (Fe19.962+Fe2.193+Mg1.33Mn0.42)Σ23.90(Fe11.323+V0.68)Σ12(Si34.73Ti0.26Al0.20Fe0.813+)Σ36O90(OH,O)48 (one unit cell content for O = 138).

The sample of the new mineral was discovered in 1977 during an investigation of an iron deposit which has been named ‘M14’. The methods used for studying this mineral included optical microscopy, X-ray powder diffraction, selected area electron diffraction analysis, wet chemical analysis, DTA, TGA, infra-red absorption and Mosbauer spectroscopy.

Spheniscidite is a new phosphate mineral occurring in a soil profile in an area of nesting penguins on Elephant Island. It is the NH4-dominant analogue of leucophosphite and has the formula (NH4,K)(Fe3+,Al)2 (PO4)2(OH) · 2H2O. It is monoclinic, P21/n with unit cell parameters a = 9.75, b = 9.63, c = 9.70 Å, β = 102° 34′, and Z = 4. The strongest X-ray lines are 6.79(100), 5.99(90), 3.05(45), 7.62(40) Å. Spheniscidite is thought to have formed by the interaction of ammonium phosphate solutions from penguin guano with micaceous and chloritic minerals in the soil. The name is for Sphenisciformes, the order name for penguins, and has been approved by the IMA Commission on New Minerals and Mineral Names.

Moolooite, a naturally occurring hydrated copper oxalate has been identified in a sulphide-bearing quartz outcrop 12 km east of Mooloo Downs station homestead (25° 01′ 30″ S., 116° 06′ 30″ E.), Western Australia. It has apparently formed by the interaction of solutions derived from bird guano and weathering copper sulphides. Partial microchemical analysis indicates a composition corresponding to CuC2O4 · 0.44H2O. The infra-red spectrum is similar to that of the artificial compound with diagnostic absorption bands at 3490, 2975, 2935, 1980, 1940, 1660, 1365,1320, 830, 510, 390, and 315 cm−1. Powder X-ray diffraction patterns indicate a disordered structure with orthorhombic symmetry; a 5.35, b 5.63, c 2.56 Å, Z = 1. The strongest lines of the powder pattern are [d Å, I, hkl]: 3.88, 100, (110); 2.50, 30, (120); 2.33, 18, (011); 2.31, 25,(101); 2.14, 20, (111); 1.938, 18, (220); 1.787, 25, (121); 1.753, 30, (211); 1.216, 15, (112). Unindexed very weak diffuse lines on some patterns can be indexed assuming a supercell with a′ = a, b′ = 2b, c′ = 2c indicating the presence of ordered crystallites.

Moolooite occurs as micro-concretionary crusts and powder in cracks and solution cavities resulting from sulphide oxidation. It is found associated with opaline silica, gypsum, broehantite, antlerite, atacamite, whewellite, sampleite, and libethenite. It is turquoise-green in colour with similar streak, lustre dull to waxy, calculated density 3.43 g/cm3. Moolooite is composed of aggregates of generally sub-micrometre sized equidimensional crystallites with α ∼ 1.57 and γ ∼ 1.95.

By analogy with artificial copper oxalate, moolooite is constructed from infinite ribbon-like elementary structural units consisting of alternating Cu2+ and (C2O4)2− ions. These units are arranged en echelon in layers which are stacked with displacements so that octahedral coordination of copper ions is completed by oxygen atoms in adjacent layers. The minimal role played by water in the structure and composition of moolooite distinguish it from other oxalate minerals. Because of the zeolitic character of the water a general formula CuC2O4 · nH2O (0 ⩽ n ⩽ 1) appears to be appropriate.

Santafeite, known only from New Mexico, USA, is re-examined using single-crystal X-ray and microprobe techniques. The new idealized formula, consistent with space group requirements, is

(Mn2+, Fe3+,Al,Mg)8(Mn4+, Mn2+)8 (Ca,Sr,Na)12[(VO4),(AsO4)]16(OH)20 · 8H2O.

Transmission electron microscopy shows that normal chrysotile and polygonal serpentine occur together and in parallel association with balangeroite, within the slip-veins of the Balangero serpentinite. Chrysotile substitutes for balangeroite and it is later replaced by the polygonal serpentine.

The chrysotile fibres are packed together according to a rod close-packing scheme, with defects. Lattice images of the polygonal serpentine confirm the structure model proposed by Middleton and Whittaker (1976), consisting of polygonally arranged fiat layers. This structural type is probably common for serpentine minerals and constitutes a fourth main type of layer configuration in 1:1 layer silicates.

The superstructure of ganophyllite has been analysed using subcell single crystal X-ray data and electron-optical observations. The full cell (supercell), space group A2/a, a = 16.6, b = 26.6, c = 50 Å, β = 94° has the approximate formula (K,Na,Ca)6+7.5(Mg,Fe,Mn)24[Si32.5Al7.5]O96(OH)1621H2O, Z = 8. A structure is proposed in which triple chains of silica tetrahedra parallel to X form narrow 2 : 1 layers with sinusoidal Mn-octahedral sheets. The triple chains are connected laterally, and across the interlayer, by pairs of inverted tetrahedra, linking to each other into four-member rings parallel to (010). Polytypes are generated by various displacements of the inverted tetrahedra.

Metal particles in the Bachmut chondrite may be subdivided into large (hundreds of μm in size) and small (1–10 µm in size) varieties. They differ in the ratio of their constituent phases, in structure, and in chemical composition. Large particles are richer in Ni than small ones, the latter being characterized by an abnormally high Cu content. It is suggested that different pre-accretion histories were responsible for producing the various types of metal grains, and that, during post-accretion thermal history, temperatures were too low to cause elemental redistribution among the grains.