The Archaean (c. 2800 Ma) ultramafic rocks in eastern Sierra Leone cut basalt lavas and are mostly olivine-rich cumulates either iron-rich (Fo85–86) and derived from a basaltic or picritic parent, or more magnesian (Fo92–93) derived from an ultramafic melt with c. 18–25 wt. % MgO. In central Sierra Leone the ultramafic rocks are lavas predating tholeiitic basalts.

The basalts show a wide variation in Zr/Y, suggesting that garnet was present in the source region of some of these rocks but not others. This implies that melting took place at different depths in the mantle. The REE evidence for basaltic rocks in the upper part of the Nimini belt succession suggests that they were derived from a mantle source region which had already suffered melt extraction. Ti/Zr ratios in the basaltic rocks are also variable and individual belts define different trends on a Ti vs. Zr plot implying that the basaltic rocks evolved in geographically distinct magma chambers. It is likely that the basaltic rocks evolved from a parental liquid with Ti/Zr = 90 via shallow level crystal fractionation. The source region for these rocks therefore had a lower than chondritic Ti/Zr.

There are two possible models for the basaltic and ultramafic magmas in the Sierra Leone greenstone belts. First that the ultramafic and basaltic liquids were derived from mantle diapirs of differing size, but originating in the same region of the mantle. Ultramafic liquids were produced in small diapirs, which store large melt fractions, and basaltic liquids in larger diapirs which segregate larger melt fractions. A second model is based upon the double diffusion process suggested for magma chambers at mid-ocean ridges and involves a transient magma chamber from which basalts, derived from parental ultramafic liquids, are erupted, with ultramafic liquids rising directly to the surface when the magma chamber is frozen. The available data does not discriminate between these two models.

Karroo basaltic lavas of southern Malawi are divided into two groups on the basis of stratigraphy, petrography, and the data from 20 newly analysed rocks. A lower group of porphyritic lavas is notably rich in plagioclase phenocrysts and has contents of K, Ti, P, Ba, and Zr unusually high for tholeiitic basalts. They are overlain by an upper group of aphyric or sparsely microphyric lavas whose chemistry is more normal for tholeiites and is comparable with that of the Karroo dolerite dykes in Malawi. Though they outcrop in the northern part of the Karroo province, the lavas and dykes have chemical characteristics more similar to southern province rocks, adding some complexity to the concept of geochemical provinces established by earlier workers. Inter-suite variations in incompatible trace element contents and ratios indicate that the basalts of each group were derived from heterogeneous mantle sources.

Over 200 sediment samples taken from ten holes drilled in the Galapagos Hydrothermal Mounds Field during D.S.D.P. Leg 70 have been analysed for twenty-one elements. The three main sediment lithologies recognized are siliceous carbonate ooze, Mn-oxide crust, and an Fe-rich silicate (nontronite), the latter two being of hydrothermal origin. The major element composition of the hydrothermal deposits is similar in each mound hole, suggesting that formation conditions and hydrothermal solution composition have been constant both geographically and with time. The large variations which occur in the concentration of some trace elements in the Mn-oxide crusts and in transition metal ratios in the nontronite compared with the pelagic ooze suggests a hydrothermal supply to the mounds of Li, Mo, Pb, and Ba in addition to Mn, Fe, and silica.

The data are compatible with suggestions that the nontronite formed at depth in the pelagic sediment blanket by replacement of biogenic ooze, whilst the Mn crusts formed at or near the sediment-water interface. Pelagic sediments in the mounds which have not been replaced are similar in composition to pelagic sediments from non-mounds holes.

Prior to serpentinization, the ultramafic rocks of the ophiolitic Highland Border Suite were depleted harzburgites, dunites, and orthopyroxenites. They may have been the residual mantle after melting of primary lherzolite that produced the basaltic rocks of the Suite. Serpentinization of these peridotites occurred at low temperatures (75±50°C) and produced pseudomorphic-textured lizardite serpentinites in which the minor-element compositions of the primary phases were preserved in the lizardite grains. Olivine was almost completely serpentinized before orthopyroxene was hydrated. Concomitant peripheral alteration of chromespinels, during serpentinization of orthopyroxene, caused release of Cr and Al cations which were incorporated into the lizardite. Under greenschist-facies conditions (c. 350°C at 3–4 kbar), the lizardite serpentinites were subsequently metamorphosed and recrystallized to nonpseudomorphic-textured antigorite serpentinites. Postmetamorphic processes included high-level brittle deformation that resulted in fracturing and cross-fibre chrysotile vein-formation, and ductile shearing (T ∼ 200 °C, P < 2 kbar) which produced talc-chrysotile shear zones.

In the Forland Complex chloritoid is restricted to the grey and green phyllites which characterize the Scotia and Peachflya groups. The textures and compositions of the rocks and constituent minerals are described and discussed in an attempt to assess how metamorphism, deformation, and chemistry have influenced the stability of chloritoid.

Tetrahedral framework compounds, as defined in this paper, generally exist as tilted and distorted versions of ideal fully expanded structures at room temperature and atmospheric pressure. How pressure, temperature, and composition (P, T, and X) affect the tilting and distortion is critically reviewed. Although P, T, and X are generally regarded as analogous variables in their effect on framework structures there is reason to believe that they have different structural effects. In particular, an important, and frequently neglected, thermal effect is the apparent shortening of the framework bonds by the anisotropic thermal motion of the framework oxygens. The effects of P, T, and X on displacive transformations in framework compounds are reviewed with particular reference to the disordered alkali feldspars and the leucites. It seems probable from the available evidence that displacive transformations do not take place at a critical size of the framework. Displacive transformations can take place with or without a volume discontinuity and hysteresis. Furthermore, the effects of P, T, and X on a solid-solution series with a displacive transformation can be different, one variable causing a volume discontinuity and another a smooth transition.

Buddingtonite of similar composition and properties to that described from the type area, is uniformly distributed throughout the upper 600 m of strata in the Condor Oilshale Deposit near Proserpine, Queensland. The mineral, which constitutes up to 16% and averages nearly 10 % of the strata, is associated with abundant montmorillonite, siderite, and quartz as well as minor amounts of disordered kaolinite, illite, calcite, pyrite, cristobalite, and an unnamed species of the jahnsite group. The buddingtonite is concluded to be of diagenetic origin. It developed in an ammonium-rich environment, most probably at significant depth within the mud beneath a stratified lake. Its progenitor, however, remains unknown. The occurrence of this mineral is also of interest in that ammonia could prove an important by-product in the commercial exploitation of the oilshales.

The chemistry of spinels, plagioclase, and iron-rich, normally zoned pyroxene and melilite from some metallurgical slags has been investigated by electron microprobe analysis. Minor element partition coefficients, some of which are composition-dependent, have been calculated from the analytical data. The pyroxene/liquid partition coefficients range from 4.03 to 0.03 in the order Ti/Zr, Al, Mn, Zn, Ba, Sn, Na, reflecting increasing incompatibility. The spinel/liquid partition coefficients range from 40.89 to 0.02 but in the order Ti, Ni, Mg/Zn, Al, Mn, Cu, Sn, Zr. However, Sn becomes very compatible when the pyroxene and spinels crystallize in association with cassiterite. Melilite greatly discriminates against the incorporation of minor elements into its crystal structure. The crystallization of these phases produces residual liquids enriched in Na, Mn, Zn, Sn, Ba, W, and Pb.

Clinopyroxene solid solutions crystallized at Ptot = 2 kbar in the natural system phonolitic tephrite-H2O (lava type from Etna eruption 1971) indicate a linear increase of ln Xcpxcats with H2Oliq %. After coupling this with the In Xcpxcats pressure dependence found through experiments, a simple relation has been set up for clinopyroxene- and plagioclase-bearing magmas. This relation allows us to calculate the amount of water dissolved in the melt, at any known pressure in the crustal range.

Electron microprobe analyses of almandine-spessartine garnets from pegmatites and aplites from the Hub Kapong batholith and Phuket Island in peninsular Thailand show three types of zoning. Garnets from pegmatites show extreme zoning, with Mn-rich cores (⋍ 80 % spessartine) and Mn-poor rims (⩾ 40 % spessartine), whereas those from aplites are either unzoned (35–40% spessartine) within the limits of detection, or have Mn-enriched rims (cores 45 %, rims 55 % spessartine). The origin of the three types of zoning is considered to reflect different crystal growth histories in each case. The pegmatitic garnets grew under conditions favourable for the development and preservation of marked concentration gradients—low nucleation density, rapid growth rate and slow cation diffusion rates for the crystal and rapid diffusion rates for the pegmatitic liquid. The aplitic garnets had a more complex growth history, with slower growth rates and faster diffusion rates for the crystal, coupled with slower diffusion rates within the aplite magma, tending to prevent the formation and preservation of concentration gradients. Subsequent resorption of aplitic garnets at lower temperatures gave rise to Mn-rich rims because of the preferential retention of Mn by the garnet; lower cation diffusion rates within the crystal permitted these marginal concentration gradients to be preserved.

Cr micas identified as chrome phengites occur in association with other Cr-rich minerals in a peculiar schist which lies along a complex shear zone within the pre-Caledonian Erris Complex. The schist generally has a chaotic internal structure but locally there is a crude planar mineralogical zoning with a serpentinebearing zone structurally above a Cr mica zone. Chemical analyses indicate that the schist is a tectonic derivative of a mixture of rock with a pronounced metasomatic character.

Chemical analyses and structural formulae of biotites from the Zaër pluton, a zoned granitic body in the Central Hercynian Massif of Morocco, are presented. The pluton grades from more mafic single-mica granodioritic facies near the margin to more felsic two-mica granitic facies in the central part. There is a relationship between the composition of the biotites and that of the host rocks. Biotite composition in the internal two-mica facies was influenced by a hydrothermal phase.

The infra-red spectrum and X-ray powder pattern of a chemically analysed specimen of leadhillite, a lead carbonate sulphate hydroxide mineral from Leadhills, Scotland, are shown to be different from those in the literature. The IR spectra of several specimens suggest that mutual replacement of SO4, CO3, and OH may occur in this mineral, and it is thought that this might be responsible for the observed variation in X-ray spacings.

Small crystals of babingtonite and rare sphene occur in a coarse-grained aggregate of fluorapophyllite, stilbite, and calcite, infilling a late-stage cavity in granodiorite from Harcourt, Victoria. This is the first reported occurrence of babingtonite in Victoria. The assemblage crystallized from fluids in which Ca and F were significant and under P–T conditions of the order of 0.5 kbar, 100–150°C. Some of the fluorapophyllite has been altered to opaline silica suggesting that the residual solutions were acidic.

An unnamed Fe3+ analogue of hematolite is described from Sterling Hill, New Jersey and Långban, Sweden. Eight microprobe analyses are in good agreement with ratios derived from a prior analysis which yielded: Al2O3 0.24, Fe2O3 10.85, MgO 10.61, MnO 41.76, As2O3 6.65, As2O5 15.29, H2O 13.23 (rem. = 1.63), sum = 100.26 %. Single-crystal study indicated that this compound is hexagonal with a = 8.28 Å, but the value of c could not be well-defined due to complex polytypism giving rise to diffuse and poorly resolved reflections along c*. In one case, a value of c = 72.69 Å was dominant. All values that could be determined were multiples of approximately 12 Å. The strongest lines in the X-ray powder diffraction pattern are: 2.400(100), 1.563(100), 6.09(80), 3.42(50), and 5.13(50). This compound is dark red and occurs as platy hexagonal crystals in clusters associated with a wide variety of species in varied assemblages. It remains unnamed because of the ambiguity arising from polytypism.

Bostwickite, CaMn63+Si3O16-7H2O, is a new species from the Franklin Mine, Franklin, New Jersey. Chemical analysis yielded MgO 0.9, CaO 5.1, Mn2O3 56.3, Fe2O3 0.5, Al2O3 1.0, As2O5 1.0, SiO2 20.1, H2O [15.1], sum = 100.0%. This yields (Ca0.76Mg0.19)Σ0.95(Mn5.973+Fe0.053+)Σ6.02(Si2.80Al0.16As0.075+)Σ6.02(Si2.80Al0.16AS5+0.07)Σ3.03O16·7.01H2O, corresponding to the idealized formula. The strongest lines in the X-ray powder diffraction pattern are (d, I): 11.3, 100; 3.548, 30; 2.898, 30; 2.567, 40; 2.262, 25; 2.238, 25; 1.470, 25. Bostwickite is dark red in colour; hardness c. 1 (Mohs'); density (meas.)= 2.93 g/cm3. It occurs in radial aggregates of acicular compound crystals. Optically, bostwickite is biaxial negative with 2Vα = 25deg; α = 1.775, Β = 1.798, γ = 1.800;, dispersion strong, r > v; strongly pleochroic with α = β redbrown, γ = yellow-brown; absorption is α = β = γ. Bostwickite is named in honour of Richard C. Bostwick, collector and compiler of data on the minerals of Franklin and Sterling Hill.

Munirite was found in the sandstones of Siwaliks formation of mid-Miocene to Pleistocene age. It occurs as small globular clusters of acicular crystals (2 to 3 mm long). Analysis gave V2O5 67.46, N2O 22.91, and H2O 10.26%. The X-ray powder diffraction pattern shows remarkable similarity to a synthetic compound NaVO3 · 1.9H2O (Lukacs and Strausievici, 1962).

Tristramite, a new mineral of the rhabdophane group, has the composition (Ca0.54U4+0.29Fe3+0.17)Σ1.00 [(PO4)0.79(SO4)0.12(CO3)0.07]Σ0.98·1.77H2O. It occurs as a late-stage replacement or matrix to brecciated uraninite (var. pitchblende) associated with sulphides in hydrothermal veins related to Hercynian granites in south-west England. It is hexagonal, space group P6222, with a 6.913 ± 0.003 Å and c 6.422 ± 0.006 Å. The strongest lines of the indexed powder pattern are 2.99 (100), 2.83 (100), 2.14 (50), 1.850 (50), 5.99 (40), 4.37 (40), 3.46 (30). For comparison, new indexed powder data for rhabdophane from Fowey Consols, Cornwall, are included. The mineral is pale yellow to greenish yellow, uniaxial positive with ω 1.644 and ε 1.664, and does not fluoresce in either short-or long-wave ultraviolet light. The habit is acicular or fibrous and no cleavage has been observed. Density (g/cm3) 3.8–4.2 (meas.), 4.18 (calc.).

Zeophyllite, a rare calcium silicate, occurs at Monte Somma, Italy, as milky-white, slightly fibrous spherules associated with apophyllite on the surface of pumice in a welded tuff dated 472 AD. The chemical analysis and the indexed powder pattern, along with the chemical formula and unit cell dimensions calculated from these data, are given. The deficiency of Ca and Si cations and the abundance of (OH) and F anions in the chemical formula calculated on the basis of 38 anions (O + F) is interpreted as due to the presence of (O4H4) substituting for (SiO4) tetrahedra and of fluorine instead of oxygen atoms in two anionic sites.