The nature of the upper mantle below the ancient cratonic areas can be deduced by study of the xenolith suites in kimberlites. Studies on the proportions of xenoliths, together with their mineralogy and chemistry, suggest an upper mantle containing an upper harzburgite zone and a lower lherzolite zone, with both of these zones containing chemical and mineralogical variants, together with minor rock types such as glimmerites, MARID-suite rocks, pyroxenites, and eclogites. Isotopic studies of the phases in xenoliths have yielded restricted ranges of values for the isotopic composition of hydrogen, carbon, oxygen, and sulphur which are tentatively identified as the true isotopic values for these elements in the upper mantle. In addition, recent discoveries suggest that diamond may be a primary uppermantle phase.

The textures and fabrics of the xenoliths indicate that plastic deformation has taken place in connection with the intrusive kimberlite event, and also in earlier events unconnected with the kimberlite event. In addition, brittle fracture has been observed, this fracturing often being accompanied by the filling of the ensuing veins and joints by fluids that have crystallized potassium-, titanium-, and water-rich phases; limited metasomatism of peridotite wall rocks accompanies this vein filling and more widespread pervasive metasomatism may also be present.

Although most upper-mantle rocks are now metamorphic, in some rare instances there are relics of earlier rock types that have not been completely obliterated by subsequent metamorphic events; most of these could be attributed to an igneous origin and in most cases during subsequent metamorphism the original rock types have been subjected to increasing pressures and/or lower temperatures.

Although the source of most materials now present at the earth's surface can be directly attributed to some identifiable source within upper-mantle rocks, no source has yet been identified for CO2, N, P, and the rare gases.

This paper discusses the relationship between the chemical composition of basic melts and the temperatures at which olivine, clinopyroxene, and plagioclase begin to crystallize at one atmosphere. Diagrams are given which show the correlation between crystallization temperature and melt composition and which allow some of the temperatures to be estimated. Because the relationship between melt composition and crystallization temperature is virtually linear over short compositional ranges, the data available can be subdivided and examined by linear multivariate statistical techniques. The result is a set of equations which permit the crystallization temperatures to be calculated with an average error of less than 6 °C and a maximum error of 27 °C. These equations have been tested by experimental determination of crystallization temperatures for a range of rocks from the Marquesas Islands.

Grunerite asbestos (var. amosite) from Penge, Transvaal, contains lamellae consisting of multiple-chain I-beams which frequently terminate within the structure. Such terminations may be either coherent or incoherent, the latter involving disturbances of the structure akin to dislocations. These may be of the nature of edge dislocations or of dislocations having both edge and screw components.

Models are presented which have been used to elucidate the structural disturbances associated with the termination and side-stepping of multiple-chain lamellae. Odd-multiple-chains are shown to be of particular significance in giving rise to dislocations with a screw component along the c-axis.

A range of sodic pyroxenes (Jd78Ac2Aug20Jd24Ac9Aug67) from the Nybö eclogite pod, Norway, have been examined by electron-microprobe analysis and by transmission electron microscopy.. Five different microprobes give generally compatible results and new analyses completely fill the natural composition gap in jadeite-rich omphacites with ∼ 3–12% acmite, confirming complete miscibility at high temperatures (⩾ 700 °C). Crystals with omphacite compositions around jadeite: augite = 1:1 contain antiphase domains resulting from the C2/c → P2/n cation ordering transformation. Exsolution microstructures were not observed, from which it is concluded that there are no two-phase regions separating the P2/n and C2/c stability fields at high temperatures (∼ 620–750 °C) and that cooling was too rapid for exsolution to occur in the jadeite/omphacite and omphacite/augite low-temperature solvi. Crystals whose compositions depart significantly from Jd:Aug= 1:1 have weak, diffuse h + k = odd reflections in selected area electron diffraction patterns which are interpreted as being due to short-range ordering outside the true P2/n stability field. The short-range ordering and lack of exsolution are consistent with a previous suggestion that the order/disorder transformation in omphacite is second (or higher) order in character. The average antiphase domain sizes (up to ∼ 3500 Å) are larger than any previously recorded in omphacites and are consistent with available petrological evidence for a long period of annealing at high temperatures before tectonic uplift and cooling.

Veins in the Central Aar granite consisting of zoisite, plagioclase, albite, alkali feldspar, muscovite, tremolite, quartz, and calcite are described. The zoisite is a thulite with up to 0.20 wt% MnO. It is argued that the zoisite is derived from granite plagioclases and has recrystallized in veins during alpine greenschist metamorphism. By later increasing XCO2 or decreasing temperature zoisite decomposed to calcite, plagioclase, and muscovite.

Thulites from different localities were investigated by X-ray and by electron microprobe analysis. Both orthorhombic and monoclinic members of the epidote group having low MnO contents have been described as thulites. It is suggested that low MnO values in the range 0.05 to 0.9 wt% cause the pink colour of thulites, regardless of symmetry.

Taneyamalite, (Na,Ca)(Mn2+,Mg,Fe3+,Al)12 Si12(O,OH)44, is a Mn2+-dominant analogue of howieite, and has been found in the metamorphosed bedded manganese ore deposit of the lwaizawa mine, Saitama Prefecture, Japan. It is triclinic, P1 or P, a 10.198(1), b 9.820(1), c 9.485(1) Å, α 90° 30(1)′, β 70° 32(1)′, γ 108° 34(1)′, Z = 1. The strongest X-ray powder diffractions are: 9.29(80)010, 7.99(35)10, 4.62(50)020, 3.65(40)120, 3.273(100)30, 3.081(50)11, 2.790(35)31, 2.630(28)023, 2.216(35)014, 43. Taneyamalite occurs in association with minor bannisterite as small seams in a caryopilite mass or as a fissure mineral cutting a hematite-quartz mass. It is greenish grey-yellow, lustre vitreous. Streak light yellow. Cleavage {010}, perfect. H. (Mohs) about 5. Calculated sp. gr. 3.30 (on unit cell data and normalized empirical formula), 3.25 (after the Gladstone-Dale Law using the revised data of Mandarino, 1976). It is optically biaxial negative, 2Vα about 70°. The refractive indices: α = 1.646(2), β = 1.664(2), γ = 1.676(2). Extinction is nearly parallel, sign of elongation positive. Pleochroism distinct: α = β nearly colourless, γ pale yellow. Absorption: α ≈ β < γ.

Probably first found in Arabia, then Moctezuma, Sonora (the type locality), finally at Tombstone, Arizona. Crystals are cubic, invariably octahedral in habit, up to 2 mm in size. Colour forest green (RHS 136A), H = 3, D = 6.4.

Wet chemical analysis gave CuO 11.0%, PbO 33.0, TeO2 50.7, H2O 3.4; soluble in cold dilute acids. The strongest lines are 7.223(5), 4.170(2), 3.614(3), 3.472(4), 3.343(6), 3.036(10), 7.952(3), 2.454(5) Å. The cell indexes as cubic, a = 12.519 Å; for Z = 12, ρcalc = 6.41 g/cm3. May be anisotropic in thin section with birefringence up to 0.011; n = 2.04.

A new magnesium aluminium phosphate mineral with the ideal formula Mg5Al12(PO4)4(OH)22·nH2O (n ⋍ 32) has been named aldermanite. It occurs as minute talc-like flakes, partly as an alteration product of fluellite, thinly coating cracks and cavities in a brecciated metamorphosed rock phosphate at Moculta, South Australia. Strongest X-ray diffraction lines are 13.40 Å (100) 002, 7.98 Å (80) 011, 5.55 Å (60) 210; unit cell parameters a= 15.00±0.007, b=8.330±0.006, c= 26.60±0.01 Å, Z = 2.

The origin of hydrous cordierite from a granulite-facies terrain in the Strangways Range, Central Australia, reported by Wilson (1978) is reviewed. In the light of geochemical and microstructural evidence for a metasomatic episode which affected the terrain subsequent to the growth of the cordierites, it is contended that the hydrous character of the cordierites results from hydration of the cordierite at this time. Extraneous argon also recorded in these cordierites may either have been incorporated into the cordierites at this time or at a later stage in the history of the terrain due to partial loss of radiogenic argon from micas which grew during the metasomatic episode. Furthermore, in view of the history of these cordierites, oxygen isotope values for the cordierites reported by Wilson are likely to be anomalous, and the isotopically light oxygen in the host granulites recorded by Wilson and Baksi (1978) probably reflects exchange with the metasomatic fluids which permeated the terrain.

The thermal expansion of iron end-member staurolite has been studied by high-temperature powder X-ray diffraction methods and by modelling with the Distance Least Squares (DLS) computer program. The X-ray approach was complicated by dehydroxylation of the staurolite. Mean linear expansion coefficients for the a, b, and c cell edges of dehydroxylated staurolite determined by the X-ray method are (× 10−6 °C−1); 20–500 °C, 8.93, 8.23, and 7.95, respectively, and 20–800 °C, 7.85, 9.43, and 9.13, respectively. Expansion coefficients of a, b, and c calculated for hydroxylated staurolite using the DLS program over the same temperature ranges are (7.86, 7.18, and 7.55 × 10−6 °C−1) and (7.87, 7.17, and 7.57 × 10−6 °C−1). The good agreement between the results from the two methods supports the use of computer modelling in estimating the thermal expansion behaviour of complex structures. The latter approach could be preferable for studying hydrated minerals.

A rich vein of silver and silver-lead sulphosalt minerals was discovered in 1906 in the Meerschaum Mine, on the Sunnyside goldfield at Mt. Wills, in northeastern Victoria. Andorite, miargyrite, tetrahedrite (freibergite), owyheeite, and argentian gold are the main silver-bearing minerals present, and sphalerite, pyrite, arsenopyrite, and covelline also occur in the vein.

The vein was probably emplaced under epithermal conditions from ore fluids accompanying the intrusion of the Mt. Wills granite. The main silver-bearing minerals were probably deposited at temperatures ranging from about 350 ° to below 300 °C.

New mineral data for kyanite-bearing eclogites supplement existing data for eclogite nodule suites from the Roberts Victor and Bellsbank kimberlite intrusions, South Africa. Calculation of equilibration temperatures using the refined KD calibration of Ellis and Green (1979) indicates that the majority of these eclogites equilibrated over a considerably narrower range (940–1185 °C) than implied by earlier estimates which did not take account of the influence of the Ca-component of garnet on KD. Most of the Roberts Victor diamondiferous eclogites appear to have equilibrated in the lower part of this range, whilst the equilibration temperatures for the Roberts Victor diamond-free eclogites extend to higher values than those from Bellsbank. The petrogenetic implications of the (calculated) temperature and pressure equilibration conditions for these eclogite suites are discussed with particular reference to possible uppermantle geotherms and available data on the graphitediamond transition boundary.

Högbomite from Reedy Creek, South Australia, is of a composition outside the previously reported range. It contains less Ti and Mg and more Al and total Fe, with a total Fe/(total Fe + Mg) value between 0.69 and 0.72. The högbomite occurs in unusual cordieritesillimanite aggregates containing minor magnetite, ilmenite, hematite, corundum, and hercynite.

Wollastonite is reported, for the first time in Iceland, in hydrothermally altered basaltic rocks in the Krafla high-temperature geothermal area, northern Iceland. Two possible modes of origin are suggested: (1) A contact metamorphic origin at the expense of hydrothermal quartz and calcite near the margins of dykes. (2) A hydrothermal origin at depths below 1000 m where fluid temperatures exceed 300°C.

FREE energies of formation of boleite, Pb26Cu24 Ag9Cl62(OH)47·H2O, and pseudoboleite, Pb5Cu4 Cl10(OH)8·2H2O, have been determined from solution studies at 298.2 K. ΔG°f values for the minerals are −19097.9±4.1 and −3705.4±5.5 kJ mol−1 respectively. These values, together with results of earlier studies (Humphreys et al., 1980) have been used to construct the stability field diagram shown in fig. 1. The boundaries for boleite and pseudoboleite are shown separately. If fields for the two minerals are plotted together, boleite has no thermodynamic stability at the silver ion activity chosen. At higher activities of Ag+(aq) the boleite field is negligible in extent.

The results can, however, be rationalized in terms of kinetics of mineral formation, rather than thermodynamic considerations alone. Since pseudoboleite is never found without boleite upon which it is observed to grow epitaxially (Winchell, 1963), it is clear that boleite must form metastably prior to any pseudoboleite deposition. Accordingly, boleite has a large range of solution compositions, from which it may precipitate. The hatched area of fig. 1 shows this at the Cu2+(aq) and Ag+(aq) activities chosen. The field is terminated at high aCl− by the AgCl line, above which silver is precipitated as AgCl(s), chlorargyrite.

It is also evident from the chemical studies that the deposition of several assemblages in the leadcopper-chloride group of minerals is simply related to variations of chloride activity. With decreasing aCl− the associations cumengeite + boleite + pseudoboleite, diaboleite + boleite + pseudoboleite, and diaboleite + chloroxiphite are expected in turn. This relationship is apparently borne out by field observations of occurrences of the minerals.