Chemical compositions, unit-cell contents, and optical properties of six clinopyroxenes from the Upper Layered Series are presented. There is a gradual enrichment in iron upwards in the intrusion although there is no measurable effect on the optical properties, possibly because of Cr variation and exsolution of Fe and Ti as oxides. The chemistry of the clinopyroxenes is consistent with crystallization from a water-rich magma of transitional nature between tholeiite and alkali-olivine basalt. X-ray oscillation photographs of single crystals reveal the presence of sub-microscopic exsolution lamellae of pigeonite, a feature consistent with the transitional nature of the parent magma. Exsolution lamellae of titanomagnetite are ubiquitous and were formed at subsolidus temperatures in response to high buffered oxygen fugacity. Comparisons are made between the properties of clinopyroxenes from the Lower, Middle, and Upper Layered Series, and the conditions of crystallization of each series.

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.

Most of the granitic sheets and veins in the Loch Coire migmatite complex do not have chemical compositions in accordance with a formation by local anatexis. Regional metasomatism by fluids from outside the exposed confines of the complex was an important factor in the development of the sheets and veins, although there was probably some overlap with magmatic conditions.

The structural formula of stilpnomelane averaged from 37 representative literature analyses and based on the determined structure is (Ca,Na,K)4(Ti0·1Al2·3Fe35·5Mn0·8Mg9·3)[Si63Al9](O,OH)216·nH2O. Ferrostilpnomelanes have up to 12 R3+ cations in the octahedral sheet, ferristilpnomelanes commonly have between 24 and 30 R3+ cations, rarely up to 37. The two groups can be distinguished by accurate X-ray powder diffraction, ferrostilpnomelanes having d001 less and a greater than have ferristilpnomelanes. The unit cell is triclinic, a = b∼21·8 Å, γ = 120°, d001∼12·2 Å, P. Hexagonal groups or ‘islands’ of 24 silicon-oxygen tetrahedra co-ordinate to the octahedral sheet, the centres of the ‘islands’ are displaced by 5a/12, 8b/12 on either side of the octahedral sheet as a result of warping of this sheet to permit articulation with the smaller tetrahedral sheet. The 24-tetrahedra ‘islands’ are linked laterally by 6-member rings of inverted tetrahedra, which in turn link at their apices to like rings connecting the next sheet of ‘islands’. Thus a single tetrahedral layer is 4 tetrahedra thick and has symmetry 6/m. The 6-member rings of tetrahedra act as hinges permitting up to 0·5 Å extension or contraction of the tetrahedral sheet to accommodate variations in the octahedral sheet dimensions with varying R2+/R3+ ratio.

Aggregates of clinopyroxene in some doleritic lavas have external outlines strongly reminiscent of garnet crystals. They cannot be satisfactorily identified either as Upper Mantle fragments or as cognate synneusis aggregates, and it is suggested that they may have developed by inversion from original garnets, which crystallized at very high pressures. Neither morphology nor composition can provide conclusive proof of their original nature, but there is circumstantial evidence from the presence of an unusual inclusion suite in basalts nearby. The commonest phases are zircon and corundum, minerals more usually found in kimberlites than in basalts. Corundum in kimberlite inclusions is almost invariably accompanied by calcium-rich garnet, which adds some significance to the suggestion that these clinopyroxene aggregates are pseudomorphing original garnet.

Fenitized quartzites are described from three localities around the Borralan alkaline igneous complex. Chemical and electron-probe analyses of amphiboles, pyroxenes, micas, and feldspars are given. Early-formed amphiboles are calcic, but these are replaced by alkaline varieties with increasing fenitization. Rock analyses indicate a ‘straight line’ rate of increase of Ti, Fe2+ + Fe3+, Mg, Al, K, and a more variable increase of Ca and Na atoms, at the expense of Si atoms. The simple composition of the unaltered quartzite allows the accurate calculation of bulk changes during fenitization. The final product of the alkali metasomatism is a syenite lying close to the albite-orthoclase minimum though the primary source of the fenitizing fluids was probably a highly potassic magma.

Chemical analyses of nine K-feldspars and thirteen albites, along with their optical, physical, and X-ray data are presented. The obliquity values Δ = 12·5(d131-d13¯1) of the K-feldspars are found to be independent of the contents of silica and volatiles in the rocks. The role of temperature as the primary factor affecting the obliquity values is stressed. The relationship between the (An + Ab) content of the potassic phase of K-feldspars and 2Vα is shown diagrammatically.

The angular relationships among sets of olivine plates in barred chondrules were investigated on the universal stage to test a suggestion that such chondrules represent exsolution and inversion from a pre-existing jadeitic pyroxene. In one of sixty-seven cases studied, adjacent plates represent olivine twinning on (100); the others vary randomly and correspond to neither olivine nor pyroxene twinning. On this basis and from other evidence, we conclude that the mineralogy and texture of barred chondrules are primary and due to rapid crystallization of ultrabasic magma in a low-pressure environment.

Talc-kyanite-quartz schists, Mg-chlorite-kyanite-quartz schists, kyanite gedritites, and kyanite-bronzite gedritites occur in the Central Province of Zambia. Experimental work in the system MgO-Al2O3-SiO2-H2O suggests that these assemblages formed at pressures in excess of 10 kb.

Equilibrium relations of lead-tin sulphides in the system SnS-PbSnS2 were studied using a sealed silica-tube technique. A complete series of solid solutions forms in the system, and lattice parameters were found to vary lineally with composition. The melting temperature of the solid solution decreases with increasing amount of PbS from herzenbergite at 880 °C to teallite at 725 °C.

Evidences were found to indicate the existence of this series of solid solution in ore deposits.

Chemical analyses and physical properties are given for six samples of beryl from greisenized granites, pegmatites, and beryl-quartz veins in the Rosses granite complex. The beryls studied were all very similar in composition and contain significant amounts of alkali elements and water in addition to the constituents represented by the formula Be3Al2Si6O18. Calculation of the empirical unit cell contents indicates that most of the H2O+ is present in the mineral as water molecules. The effects of these extra constituents on the physical properties are discussed, and it is suggested that the variation in refractive indices displayed by beryl is to a large extent attributable to the variable water content.

The pyroxenite of Nero Hill has been metamorphosed under relatively low water pressure at the centre and higher water pressure at the margins. Thus a central pyroxenite consisting of diopside, hypersthene, oligoclase, garnet, and a little hornblende grades outward into a hornblende-cummingtonite amphibolite.

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.

A 250 µm olivine crystal in Sharps contains 1 to 5 µm insets identified by microprobe analysis as ferroan monticellite, spinel, and fassaite with average compositions: olivine (host), (Fe0·44Mg1·51Ca0·05) (Si0·99Al0·01)O4; ferroan monticellite, (Ca0·89Fe0·41Mg0·66) (Si1·00Al0·02)O4; spinel, (Fe0·41Mg0·59)(Fe0·063+Cr0·23Al1·69Si0·01Ti0·01)O4; and fassaite, Ca0.96(Fe0·01Mg0·59)(Al0·18Ti0·07Fe0·163+)(Si1·53Al0·47)O6. Textural and experimental data suggest early crystallization of spinel from a calcic olivine melt, exsolution of ferroan monticellite from the host olivine, and reaction of spinel and ferroan monticellite to form fassaite. The severe depletion of alkalies and silica in this crystal suggests it is a residue from vapour fractionation.

The net cationic charge of the octahedral and tetrahedral layers was calculated from the analyses of 100 biotites and 93 muscovites and compared to the observed hydroxyl contents (OH+F+Cl). The correlation coefficient between these parameters of −0·96 for biotites and −0·82 for muscovites demonstrates that the hydroxyl content in these micas varies in response to cationic substitutions. Thus substitutions in micas involve cation-hydroxyl replacement couples in addition to other modes previously recognized. Tetrasilicic phlogopite, K2Mg6Si8O22(OH)2, which is related to phlogopite by the substitution Al3+ + H+ = Si4+ was synthesized but is not a stable phase under the conditions investigated. This mica crystallizes as a 1M polymorph with a = 5·289(2) Å, b = 9·151(3) Å, c = 10·247(3) Å, β = 100°4(2).

Exchange reactions, such as Al3+ + H+ ⇌ Si4+, between phlogopite and pyroxenes at depth may provide a mechanism for release of H+ within the mantle.

The oxidation of amosite, crocidolite, and biotite has been determined at temperatures up to nearly 900 °C under both a vacuum (10−2 mm Hg) and oxygen (10 and 600 mm Hg). Infrared spectra gave the loss of constitutional hydroxyl under these conditions. The loss of tensile strength of the amphiboles with increasing temperature seems to be due to thermal decomposition. For the three minerals oxidation takes place progressively over a broad temperature range. Under vacuum there is a certain temperature above which the ferric iron previously formed is reduced; this temperature corresponds to the completion of the loss of hydroxyl. The crocidolite anhydride in the literature is most probably an oxycrocidolite formed by dehydrogenation, the truly dehydroxylated zones being amorphous.

Low Ceylon zircons showing an optical absorption band at 5200 Å appear to have suffered more radiation damage than other low Ceylon zircons. Very heavy fission-fragment irradiation failed to lower the density of each of two low Ceylon zircons significantly, although the specimens were rendered completely amorphous. Further fission-fragment irradiation experiments indicated that low Ceylon zircons showing a previously reported anomalous absorption spectrum have been heated late in their geological histories.

Unit-cell dimensions and refractive indices of lithium-iron micas decrease with decreasing iron and increasing lithium. Indices β and γ as well as parameters a and b can be used to estimate the composition of lithium-iron micas but basal spacing and 2Vα are poor indicators of composition.

The chemical composition of natural lithium-iron micas from the Krušné hory and the Erzgebirge along the Czechoslovak—German border was discussed in Part A of this study (Rieder et al., 1970). It was concluded that the composition and crystallography of these micas fit best the series siderophyllite-polylithionite. The compositions were expressed by the ratio A′ = LR/(LR+‘Fe’). In this expression, LR is the subscript value of Li or octahedral R3+ (whichever is the smaller) in the crystallochemical formula, ‘Fe’ is the sum of the values in the formula of Fe2+ and Mn2+. A′ therefore defines the position of a particular mica on the siderophyllite-polylithionite join. This paper deals with the correlation between composition, cell dimensions, and refractive indices.

New analyses are given of granites from 23 intrusions in Scotland, Ireland, and the Isle of Man. Together with existing analyses, these were used to measure the regional variation in composition of Caledonian granites by means of trend surface analysis. An explanation of the variation is presented that involves the production of magma by melting in the crust, at a depth determined by the geothermal gradient.

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.