Bahianite, Sb3Al5O14(OH)2-Sb3Al5(Al, Be, Si)<2O16, monoclinic, a 9·406(6), b 11·541(8), c 4·410(3) Å, β 90·94(3)°, Z = 2, space group C2/m, is a new species from the Paramirim region, south central Bahia state, Brazil. It occurs as water-worn pebbles (‘favas’) with quartz, andalusite, kyanite, diaspore, eskolaite, cassiterite, etc. Colour tan to cream, crystals in vugs colourless, tan or pale violet. Specific gravity ranges from 4·89 to 5·46 (5·26 g cm−3 for Sb3Al5O14(OH)2); hardness 9, cleavage {100} perfect, lustre adamantine, biaxial (−), 2V large, α = 1·81, β = 1·87, γ = 1·92, dispersion r > v.

The crystal structure represents a new type and is based on hexagonal close-packed oxygens. It is related to the structure of simpsonite Ta3Al14O13(OH).

Tlapallite is a new mineral found in 1972 at the Bambollita (La Oriental) mine near Moctezuma, Sonora. Also recently found in old specimens from Tombstone, Arizona. Data for type (Mexican) material: Colour viridian green RHS-128A with pale streak, H = 3, D calc = 5·05 g/cm3. Crystals monoclinic, class unknown. Indexing based on Ito method gave a cell: a = 11·97 Å, b = 9·11, c = 15·66, β = 90 ° 36′. Strongest lines: 11·972 Å (10), 2·985 (10), 3·540 (6), 5·946 (5), 2·887 (5), 4·731 (4), 3·372 (4), 3·282 (4). Similar data obtain for Tombstone. Chemical analysis for type material yielded the formula H6Ca2Cu3(SO4)(TeO3)4,TeO6 with Te4+:Te6+ = 4:1. However, analysis of the Tombstone material indicates a more general formula H6(Ca, Pb)2(Cu, Zn)3(SO4) (TeO3)4,TeO6. The better data from this material indicate Z = 4, D calc = 5·465 vs D meas = 5·38. Characterized by extreme birefringence, α = 1·815, β = γ = 1·960; for Tombstone α = 1·955, β = γ = 2·115.

Named from the Nahua word tlapalli, meaning paint, in allusion to its mode of occurrence at the type locality.

The distribution and geochemistry of loveringite, an accessory Ti, Fe±Cr oxide containing U and rare-earth elements (Ln) from the Jimberlana Intrusion, have been studied. Loveringite is most abundant in bronzite cumulates; it is found in trace amounts in early plagioclase-augite-hypersthene cumulates, but is not found in the olivine cumulates or in the late-stage differentiates. Loveringites from the bronzite cumulates have a high Cr content compared with those from the plagioclase-augite-hypersthene cumulates, suggesting that the mineral is stabilized by the presence of Cr in the intercumulus liquid. The Ln pattern shows a strong depletion trend from La to Eu, a sharp reversal between Eu and Tb and a second depletion pattern from Tb to Lu. This pattern suggests that the Ln are substituting into two sites, one much larger than the other.

The high-temperature transformation of andalusite (Al2SiO5) into 3/2-mullite (3A2O32SiO2) plus vitreous silica (SiO2) has been studied within the temperature interval from 1300 to 1600 °C by means of X-ray powder and single-crystal techniques and by infrared spectroscopy. Results are interpreted in terms of a topotactic transformation in which (011) and (01) planes of andalusite transform into (20) and (201) planes of 3/2-mullite; in this way the a- and b-axes of the two phases are interchanged. From the structural and orientational relationship between the andalusite and 3/2-mullite latrices it is concluded that the aluminium-oxygen octahedral chains, running in both structures parallel to the crystallographic c-axis, are preserved during phase transformation.

The amphibolites and mafic schists that occur in the Precambrian metamorphic rocks of the Grand Canyon are divided into five major groups: anthophyllite and cordierite-anthophyllite rocks, early amphibolites, Granite Park mafic complex, hornblende-beating dykes, and tremolite-bearing dykes. Many types of amphibole occur in these rocks. Microprobe analyses identify gedrite, anthophyllite, cummingtonite, and grunerite, as well as three groups of calcic amphiboles. These last range in composition from colourless tremo-litic or actinolitic amphiboles, through pale-green horn-blende, to strongly pleochroic green-brown hornblende, which contains a significant proportion of the tscherma-kite and pargasite endmembers. Phase relationships between the coexisting amphiboles and other minerals are presented for two regional metamorphic events. Assem-blages containing chlorite, garnet, and hornblende were formed during the first event; from the absence of staurolite, but the presence of almandine garnet and oligoclase-andesine, it is concluded that the metamorphic grade was between the upper greenschist and the lower amphibolite facies. The second period of metamorphism produced rocks of the staurolite and sillimanite zones, within which three main ‘subfacies’ can be distinguished on the basis of phase relationships in the mafic schists.

High-temperature geothermal fields in Iceland represent localized anomalies of hot, altered rock in the uppermost part of the crust, which coincide with points of maximum tectonic/magmatic activity. These points correspond to the intersection of oblique fault swarms to the plate boundaries. Geothermal activity under mid-ocean ridges follows probably similar tectonic/magmatic anomalies.

Due to high permeability sea-water invades the bed-rock of the Reykjanes Peninsula, Iceland, and is overlain by a variably thick lens of dilute ground water of meteoric origin. The variable degree of salinity of geothermal waters in the Reykjanes Peninsula has resulted from different degree of mixing of fresh ground water with the underlying sea-water-ground-water in the downflow zones around the geothermal fields. At Reykjanes the geothermal water represents heated sea-water without any freshwater mixing. The difference in the composition of sea-water or sea-water/fresh water mixtures and the geothermal waters is due to basalt/water interaction at elevated temperatures. The major-element chemistry of the geothermal water represents an equilibrium composition at the relevant aquifer temperatures. The activities of silica, calcium, sulphate, and carbonate are thus limited by the solubilities of quartz, anhydrite, and calcite. Fluoride activity is thought to be controlled by an ionic exchange reaction where it substitutes for hydroxyl groups in phyllosilicates. The ratios of individual cations and hydrogen ion are governed by ionic exchange equilibria with hydrothermal minerals, probably smectite and chlorite. The equilibrium pH for the Reykjanes and Svartsengi geothermal waters is 5·5 and 5·1 respectively. Sea-water will become somewhat acid upon heating to more than about 300 °C and equilibration with basalt, the acidity increasing with temperature.

Phosphorites from the continental shelf off Morocco have been analysed for major elements and Fe, Mn, V, Cu, Ni, Zn, As, Na, Sr, S, and for carbonate. In pyritic phosphorites Cu, Ni, Zn, and As are present mainly in minor pyrite and organic carbon. In ferruginous phosphorites As, Mn, and V are associated with goethite. In the ferruginous phosphorites Cu, Ni, and Zn may have been introduced in association with organic matter and pyrite during phosphorite formation and been retained during subsequent destruction of these phases by weathering. In all phosphorites Na and Sr are present mainly in carbonate-fluorapatite. Sulphur in the ferru-ginous phosphorites occurs only in carbonate-fluorapatite. In the pyritic samples it is partitioned between pyrite and francolite (carbonate-fluorapatite).

Tobermorite minerals vary in some proper lies, notably in whether or not unidimensional lattice shrinkage occurs by about 300 °C to give a 9·3 form; specimens that do this are called normal, and ones that do not, anomalous. Data are compared for thirteen natural tobermorites and the extent to which normal or anomalous character is related to other properties is examined. The most definite correlations found are with chemical composition and morphology. The conditions of formation of normal and anomalous tobermorites are discussed in the light of synthetic evidence.

Zincian hercynite is present in pelites within the aureole of the Ardara Pluton. The hercynite is always surrounded by cordierite, garnet, or feldspar and is never in contact with quartz. From textural and chemical evidence it is apparent that the hercynite is produced by the reaction of zincian staurolite → zincian hercynite + cordierite + sillimanite. A temperature of about 725°C at pressure of about 2·6 kb and anφo2 below that defined by the Q.F.M. buffer is postulated for this reaction.

Sedimentary analcime in a small basin in Cainozoic basalt at Murrurundi, New South Wales, has probably resulted from the reaction of Na-rich water on colloidal nontronite derived from volcanic ash. Based on cell dimension (13.713 Å) and Δ2θ(1·81) determined by Saha's (1959) method it is a Group C low-silica type of Coombs and Whetten (1967).

Analcime of hydrothermal origin occurs in the gabbros and in the amphibolites and granulites. Crystals from the different rock suites display the same unusual characteristics upon dissolution: the interior is much more susceptible to attack than the outer growth zone; the former may be converted to a skeletal boxwork, and the latter may suffer extreme differential dissolution along successive narrow growth horizons. Pseudomorphs of adularia after analcime have been found in various stages of development, from partial to complete replacement. Some of the latter preserve the very delicate dissolution structures in detail. Up to fourteen growth horizons have been detected in the outer millimetre of the crystal. This demonstrates that both the growth and dissolution of analcime occurred prior to the formation of adularia, an event that has been dated.

Tugtupite, space group 1, belongs morphologically to the crystal class 2m. The paper describes pseudotrigonal contact triplets recently found as freely developed individuals on two specimens donated to the Geological Museum, Copenhagen. The contact triplets, described as a symmetric twin, have the composition planes, which are also the twin planes, (10) and (01); the pseudo-threefold axis, along which the crystals are pronouncedly elongate, is [111]. The calculated reentrant angles on the two sides of the pseudotrigonal prism, the protruding angle on the third side, and the ‘central misfit’, expressed as the geometrical angles, are 178° 41′, 181° 20′, and 2° 39′ respectively. Tetragonal crystals forming pseudotrigonal twins are rare and it is emphasized that the pseudotrigonal habit has become apparent only because: the faces developed on individual I and on individuals II and III are not the same; and the proportion between the lengths of the traces of the faces (01) individual I and (01) individuals II and III in a plane perpendicular to the pseudo-threefold axis and the traces in the same plane of all other faces constituting the pseudo-threefold prism are 2:1.

Hydrothermal ruffles from a suite of rocks at Mount Perry, Queensland, have been studied in thin section, by electron microprobe analysis, and by transmission electron microscopy. The iron-bearing rutiles, while originally singte-phase, are found to exsolve a sequence of iron-rich precipitates on experimental annealing, with hematite being formed as the stable equilibrium precipitate. Experiments at different temperatures and annealing times enable a time-temperature-transformation plot to be drawn for the exsolution process. The kinetics of this process are used to conclude that the rutiles formed below about 450 °C.

Spectral reflectances and chemical compositions of twenty-eight different grains of exsolved titanomagnetite were measured. Relations between reflectance and composition were established by calculating best-fit planes (Kummell, 1879) for the reflectance at 499 and at 617 nm. These were then transformed to expressions from which the contents of Ti and Mg can be estimated. Even though these estimates are not as accurate as microprobe values, the method is still a useful tool in the study of chemical variation in exsolved titanomagnetites.

A method of producing platinum-iron alloy sample containers has been developed that allows experiments to be carried out on iron- and volatile-bearing systems with minimal net exchange of iron between the sample and its container. Preliminary experiments carried out using these containers in the temperature range from 1100 °C to 1250 °C and at pressures up to 10 kb over periods of up to 75 hours produced an average iron loss of 10% to 16% (as FeO) compared with more than 50% FeO loss obtained using pure platinum containers. A more judicious choice of alloy composition would reduce this loss still further.

The value of infra-red spectra in identifying sulphide minerals has been assessed by surveying the spectra of some forty specimens. Spectra of finely ground samples dispersed in polyethylene discs were obtained in the region 420-90 cm−1 with a resolution of 3–4 cm−1, using a Beckman-RIIC Fourier-Transform Interferometer. Except for minerals whose metallic conductivity obliterated vibrational features, the spectra permitted rapid recognition of sulphide minerals either alone or in mixtures.

Spectra of the following twenty-five pure, or nearly pure specimens are presented: cinnabar, galena, pyrrhotine, alabandine, sphalerite, wurtzite, realgar, orpiment, stibnite, bismuthinite, arsenopyrite, tetrahedrite, pyrargyrite, proustite, enargite, bournonite, boulangerite, jamesonite, and plagionite. Sulphides whose metallic conductivity led to featureless, almost total, absorption of infra-red radiation included chalcosine, troilite, millerite, covelline, bornite, and pyrrhotine: only the spectrum of the last is illustrated as a typical example.

Comparison of the spectra reproduced here with those previously published show a fair measure of agreement, although there are discrepancies. Povarennykh and co-workers, for example, have reported a common sequence of broad absorption bands at 370, 280, and 180 cm−1 for minerals that were found here to exhibit featureless metal-like absorption. The sources of these and other discrepancies are briefly discussed.

Tučekite, Ni9Sb2S8, was found as microscopic grains in a mineralized Archaean chlorite schist at Kanowna (35° 35′ S., 121° 36′ E.), Western Australia, and in the gold-bearing conglomerates of the Witwatersrand System (26° S., 27° E.), South Africa.

The nickel mineralization at Kanowna is located in metamorphosed basic and ultrabasic rocks of the Morelands Formation, which is part of the Kalgoorlie-Yilgarn succession of the West Australian Archaean shield. The tučekite-bearing mineralization occurs as an approximately 2 cm thick zone of disseminated sulphides in a chlorite schist near its contact with a serpentinized ultramafic intrusive rock. Tučekite is here associated with millerite, pyrite, chalcopyrite, gersdorffite, pentlandite, magnetite, and supergene polydymite. Tučekite occurs as rims and irregular grains partly replacing millerite, and was apparently formed during the later stages of the ore-forming process by reaction of Sb-bearing solutions with millerite.

In the Witwatersrand the mineral was found in a heavy mineral concentrate prepared from ore from the Vaal Reef, Vaal Reefs mine, Klerksdorp (Far West Witwatersrand), and in a mixed concentrate from the Carbon Leader Reef and the Ventersdorp Contact Reef, Western Deep Levels Ltd., Carltonville (West Wits Line). Although rare free grains of tuSekite are found, the mineral is more commonly intergrown with gold, and in the Vaal Reef the mineral is also found intergrown with gersdorffite.

Empirical formula of the Kanowna mineral is (Ni, Fe, Co)9·05(Sb, Bi, Te)1·00(Sb, As)1·04S8; that of the Witwatersrand mineral is (Ni, Fe)9·00(Sb, Bi)1·00(Sb, AS)1·06S8. The structural formula is assumed to be ; Z = 1. The mineral is opaque, has a metallic lustre, and is pale yellow. Under the microscope in reflected light it is pale brownish-yellow; bireflectance not discernible; anisotropy very strong with deep brown and greyish-blue polarization colours; reflectivity high. Indentation hardness 718 kg/mm2 (20 g load); 417 kg/mm2 (10 g load).

Strongest Debye-Scherrer powder-pattern lines of the Witwatersrand mineral are 2·76 (10) 211; 2·38 (8) 112; 2·28 (8b) 221, 310; 1·850 (8) 222; 4·33 (7) 101; 1·793 (7) 400, 3o2. By analogy with hauchecornite, the pattern can be indexed on a tetragonal unit cell with a = 7·174 Å and c = 5·402 Å; ρ (calc.) = 6·15 g/cm3. Type material is preserved in the British Museum, London, and the National Museum, Prague (Czechoslovakia).

An examination has been carried out of ten specimens assigned to the group. These include metatype specimens of neotocite (Gestrikland, Sweden) and penwithite (Wheal Owles, Penwith, Cornwall) and topo-type specimens of stratopeïte (Pajsberg, Sweden), klipsteinite (Herborn, Dillenberg, Germany), and opsimose (specimen labelled klipsteinite, but from Klapperud, Dalecarlia, Sweden). The investigation arose out of the recent find of neotocite at the Geevor mine, Cornwall, close to the site of the type locality for penwithite.

In the investigation klipsteinite has been confirmed as a mixture (Fisher, 188o), the dominant mineral in the mixture giving an X-ray pattern close to birnessite. Chemical analyses, refractive indices, and specific gravity determinations are given for the remainder in the miniprint section, p. M27 (Table I). They show that the group can be represented fairly closely by the formula (Mn, Fe)SiO3.H2O, but with significant carbonate present in each sample. CO2 has not generally been reported before in these minerals and the water content is lower than previous analyses, as a result of the precautions taken in drying the material before analysis (over magnesium perchlorate at room temperature).

The specimens examined are all dark brown or black in appearance (often darkening on exposure to light) with a vitreous lustre and conchoidal fracture. The group should be regarded as poorly crystalline since all the specimens gave similar X-ray powder patterns with three very broad and diffuse lines around 3·5, 2·6, and 1·6 Å respectively (see Whelan and Goldich, 1961). After heating to 1000 °C all form braunite, with the exception of stratopeite, which gave an X-ray powder pattern closer to pyroxmangite. Hausmannite or spinel were also found associated with braunite in several specimens.

The full text includes the results of differential thermal analysis and infra-red spectra from the samples.

Of the names used in the group, opsimose (Beudant, 1832) was the first recorded, but in this and the subsequent work of Bahr (1850), it was associated with material much richer in manganese. Wittingite and neotocite (Nordenskiöld, 1849) were -named separately on account of the higher iron content of neotocite. Stratopeïte (Igelström, 1851) is a magnesium-bearing variety, while penwithite (Collins, 1878, 1879) was thought to have a different manganese valency state from wittingite.

In view of its current widespread usage and the fact that neotocite was originally named for an iron-bearing manganese silicate it is proposed that neotocite be defined as the group of poorly crystalline manganese silicates with formulae close to (Mn, Fe)SiO3.H2O and Mn > Fe. With Fe > Mn the series grades into hisingerite. Limited substitution of MgO, Al2O3, and CO2 should be acceptable. Finally it has been proposed that the other names be discarded. The Commission on New Minerals and Mineral Names, IMA, has approved these proposals, but came to no firm conclusion as to whether the group name should be spelt ‘neotocite’ or as in the original description ‘neotokite’. Accordingly either are permissible.

Hornblendes are not common in the charnockites of Kondpalli, but occur as an important constituent in the pyroxene granulites and pyroxenites of Seshadripuram hill. Analyses and optical data for two pargasites are given.