The Galway Granite often has a highly siliceous aphyric alkali granite at the margin, followed inwards by a K-feldspar phenocrystic adamellite and then a steeply layered granodiorite. This previously puzzling arrangement, which seemed to conflict with the necessity to cool from the periphery and crystallize the most basic granite at the margin, is examined by a traverse of chemically analysed rocks and biotites. The Mg/(Mg+Fe+Mn) values indicate that the granodiorite probably crystallized from the outside inwards. The marginal aphyric granite crystallized from the acid residuum in the nearly solid adamellite. This was drawn out of the adamellite by blocks of country rock falling into the adamellite and creating a zone of rarefaction behind them. This also explains the absence of a chilled margin and the aplitic texture and mineralogy of the aphyric granite. The adamellite largely accumulated by crystal settling with gravity grading but the granodiorite crystallized in vertical layers during upward vertical movements of the magma that tipped up the gravity layering in the adamellite. Scattered microdioritic xenoliths are postulated to be disrupted dykes. Eighteen granite and twenty-seven biotite analyses are tabulated.

A gradational increase in concentration of CO2 towards the margins of a very fine-grained basalt dyke has led to the development of a pale marginal facies, enriched in carbonates, particularly siderite. Increases in CO2 from about 3 % in the interior of the dyke to 8 % at the margins are accompanied by decreases in SiO2 and Fe2O3, increases in Al2O3, and less significant changes in the other major components. Cu, Co, and Zn change only slightly, and Cr, Ni, and Li remain constant. Petrographic variation is considerable, even in the superficially homogeneous interior of the dyke, in which it ranges from a type containing a titanaugite (analysed) to one devoid of pyroxene, but containing conspicuous opaque minerals. Microprobe analysis for Fe and Ti shows that these comprise: cotahedral titaniferous magnetite; rodlets, less than 1 µm thick, of rutile partly altered to, or overgrown by, ilmenite; and sub-opaque patches with a very low Ti/Fe ratio. Plagioclase, An55, is the most abundant and constant crystalline phase in the interior of the dyke, but changes to An20 in the marginal facies. Mineral-content of the latter, deduced from optical, chemical, and X-ray data, also includes siderite, serpentine and clay minerals, leucoxene, and apatite. There is no evidence of quartz, sericite, or calcite.

Petrographic evidence shows that variations in concentrations of CO2 and H2O affected phase equilibria from the start of magmatic crystallization. Data on the fO2 required for TiO2 and Fe-oxide phases to co-exist at magmatic temperatures indicate that, initially, the concentrations of CO2 and H2O in the interior of the dyke were higher than the values recorded in analyses of the rocks. From this evidence and the field relationships, it is concluded that the intruding magma was rich in volatiles, which diffused towards the dyke margins and, in part, became trapped as the magma congealed, producing a changed marginal assemblage of minerals. The dyke provides a unique glimpse of influences on a basic magma exerted by what S. J. Shand has aptly termed the ‘fugitive constituents’, the transient effects of which are rarely preserved in the rocks.

Vincentite, a new palladium mineral containing As, Sb, and Te, has been discovered in platinum-gold concentrates from the Riam Kanan River, SE. Borneo. It occurs as small grains (up to 40 µm) in iron-bearing platinum. In reflected light, vincentite is light brownish-grey and in some sections weakly anisotropic. Reflectance at 470, 546, 589, and 650 nm is 46·3–47·5, 49·2–52·8, 51·7–53·9, and 54·9–56·0, respectively. VHN15 = 494. Electron probe analysis has been performed on two grains, the compositions of which are (Pd5·32Pt0·68) (As0·90Sb0·48Te0·65) and (Pd5·17Pt0·83) (As0·89Sb0·70Te0·45) or, simplified, (Pd,Pt)3(As,Sb,Te). This is distinctly different from both arsenopalladinite, Pd5(As,Sb)2 with As > Sb as defined by Clark (1974), and mertieite, Pd5(Sb,As)2.

The following lines have been observed in the powder pattern: 4·180, 3·950, 3·240, 2·750, 1·997, 1·749, 0·944. This cannot be matched by the patterns of arsenopalladinite, mertieite, isomertieite, stibiopalladinite, atheneïte, or synthetic Pd3As.

The name is in honour of Prof. E. A. Vincent, of Oxford.

The arsenopalladinite concentrates from Itabira, Minas Gerais, Brazil, have been found to contain three arsenide-antimonides of palladium, namely arsenopalladinite, atheneïte, and isomertieite. The second and third of these are new minerals.

Arsenopalladinite, redefined, is Pd5(As,Sb)2 and triclinic with a 7·399, b 14·063, c 7·352 Å, α 92° 03′, β 118° 57′, γ 95° 54′. Z = 6. Dmeas = 10·4, Dcalc = 10sd46. In reflected light arsenopalladinite is white with a yellowish creamy hue. The mineral shows complex polysynthetic twinning and is strongly anisotropic. Reflectance measurements at 470, 546, 589, and 650 nm respectively gave: in air, 46·67–48·86, 49·97–52·90, 52·82–54·96, and 55·61–57·72 in oil, 32·30–35·07, 37·12–39·40, 38·97–41·32, and 40·28–43·07. VHN100 379–449, av. 407.

Atheneïte, (Pd, Hg)3As, is hexagonal, space group P6/mmm and cell dimensions a 6·798, c 3·483 Å. The strongest lines of the powder pattern are 2·423 vvs (111) , 2·246 vs (201), 1·371 s (212), 1·302 s (302), 1·259 s (321). Z =2. Dcalc = 10·16. In reflected light atheneïte is white with a faint bluish tint compared to arsenopalladinite. Anisotropy distinct. Untwinned. Reflectivities for the two grains examined are: in air, 470 nm 47·51–54·75, 47·43–51·18; 546 nm 50·79–58·01, 51·36–54·36; 589 nm 53·13–61·01, 53·24–55·86; 650 nm 55·94–63·13, 54·76–56·77; in oil, 470 nm 30·03–43·67, 33·46–37·31; 546 nm 33·42–47·75, 37·64–41·07; 589 nm 35·80–49·04, 39·40–42·24; 650 nm 38·25–50·49, 41·07–42·85. VHN100 419–442, av. 431.

Isomertieite, (Pd,Cu)5(Sb,As)2, is cubic, space group Fd3m, a 12·283 Å. The strongest lines of the powder pattern are 2·356 vs (333, 511), 2·167 vvs (440), 0·8599 s (10.10.2, 14.2.2), 0·8206 s (12.8.4), 0·7996 s (10.10.6, 14.6.2), 0·7881 s (999, 1.11.1, 13·7·5, 15·3·3), 0·7801 s (12.10.2, 14.6.4). Z = 16. Dcalc = 10·33. In reflected light isomertieite is a pale yellow colour. One grain was isotropic, three others displayed weak anisotropy. Untwinned. Reflectance measurements at 470, 546, 589, and 650 nm gave respectively: in air, 44·74–46·46, 52·23–53·25, 55·05-57·49, 56·97–62·03; in oil, 31·04–31·40, 38·42–38·90, 40·80–42·16, and 42·91–45·63. VHN100 587–597, av. 592.

Quantitative colour values are also given, and the chemical and optical properties are compared with the related mineral, stibiopalladinite.

Killalaite occurs in a thermally metamorphosed limestone at Killala Bay, near Inishcrone, Co. Sligo. It is a secondary mineral and occurs in cavities and veins with calcite or afwillite in spurrite-wollastonite rocks. It is found in well-formed colourless crystals, up to 2 mm long, with a characteristic penetrative twinning observed under crossed nicols as a cross ‘bow-tie’, cleavage (100) perfect, (010) good, (001) poor. The crystals are monoclinic, biaxial, 2Vα26°, refractive index α 1·635 and γ 1·642, optic axial plane (010), β = [010] (elongation), γ: [001] ≈ 16°, density calculated from RI ∼ 2·88, provisional approximate cell dimensions a 9·3, b 9·9, c 7·7 (±0.1 Å), β ∼105° and Z = 2. Electron microprobe analysis gave CaO 57·o, SiO2 39·8; H2O (by difference) 3·2; MgO, Al2O3, and Fe2O3 together < 0·3 weight %, composition 2Ca3Si2O7.H2O. The stronger lines of the X-ray powder pattern are: 3·03, 2·824, 2·724, 2·275, 2·224, 1·688, 1·673, and 1·413 Å. It probably formed in a CO2-deficient hydrothermal environment in the PT range of 350° to 500 °C and 500 to 3500 bars. The mineral is named after the name of the locality, Killala Bay, and should be pronounced as killalahite. Type material is preserved at the Ulster Museum and at the British Museum (Natural History).

Seven manganese minerals have been observed in geodes from Chihuahua, Mexico. Ramsdellite occurs in a number of different habits, but the morphology and precession X-ray patterns suggest that it is pseudomorphous after groutite. Pyrolusite is found only in association with rams-dellite and is believed to be an alteration product of that mineral. Todorokite generally occurs as a late-stage fibrous overgrowth in many of the geodes. Ranciéite, birnessite, hollandite, and cryptomelane are present in trace amounts. This assemblage of manganese minerals is typical of supergene mineralization.

A 1 M solution of potassium permanganate was sealed in a gold capsule and was treated under conditions of temperature and pressure up to 800 °C and 2·5 kb. Different kinds of products were produced under different conditions of synthesis, and potassium manganate, birnessite, cryptomelane, hausmannite, manganosite, and a new phase appeared. The chemical composition of the new phase was determined as K2Mn4O9 and its X-ray powder diffraction pattern was indexed on a hexagonal cell with a 11·295 and c 21·870 Å.

Nahcolite (NaHCO3) is identified and recorded for the first time from an igneous rock. Often associated with it is another carbonate mineral tentatively identified as kalicine (KHCO3), which has not previously been recorded as a primary mineral in any rock. These minerals occur in inclusions in apatite crystals in ijolites and carbonatites, and indicate that both ijolite and carbonatite magma must have been considerably richer in soda and potash than is indicated by the chemical analyses of the rocks. The identification was made by a combination of microchemical, solubility, crystallographic, and optical determinations.

Tantal-aeschynite occurs as idiomorphic metamict crystals in the Raposa pegmatite at São José do Sabugí, Paraíba State, NE. Brazil. Morphological data, microscopic properties, and differential thermal analysis results are given. Electron-microprobe analyses yielded a formula: {Ca0·28(Yt,Ln)0·425(Th,U)0·11}(Ta0·75Ti0·62Nb0·595Fe0·05)O6. Yttrium is the predominant rare-earth element, with cerium and neodymium as most abundant lanthanides. The tantal-aeschynite unit cell has (after heating) a 5·34, b 10·97, c 7·38 Å. An indexed X-ray powder pattern (similar to that of aeschynite) is presented.

An occurrence of magnesian collinsite has been found with other rare phosphates in a variscite deposit in semi-desert 15 km NW. of Milgun Station homestead (25° 6′ S., 118° 18′ E.), Western Australia. The collinsite occurs as tapering white 3-mm prisms, mammillated aggregates, and thin veinlets in cavities in mudstone. The crystals have two good cleavages, D2.93, subvitreous lustre, H4–5, white streak and are brittle. Optical properties α 1·632, β 1·642, γ 1·657, 2Vγ , ≈ 80°. The mineral is triclinic with a 5·734, b 6·780, c 5·441 Å, α97·29° β 108·56°, γ 107·28°. X-ray powder data given, the lines are similar to P.D.F. card 14–314 but new cell gives better indexing. Chemical analysis by F. R. W. Lindsey gave FeO 0·07, MgO 11·3, CaO 35·2, Na2O 0·01, K2O 0·02, P2O5 41·2, H2O+10·7, H2O− 0·15, F0·02, SiO2 (quartz impurity) 1·31, Al, Mn, Zn, SO3 not detected, net sum 99·97, close to Ca2Mg(PO4)2.2H2O, after deduction of moisture and quartz impurity. Typical specimens are preserved at the Government Chemical Laboratories, Perth, Western Australia.

Oxygen partial pressures in atmospheric-pressure quench furnaces were found to vary by as much as 0·5 in log fo2 when changes were made in gas flow rate and direction suggesting that careful analysis of the gas mixture supplied to a furnace is not a guarantee of the oxygen pressure that a sample in the furnace will attain. The use of magnesiowüstite compositions, with variable oxygen contents, as indicators of oxygen pressure is described.

Growth twins, parallel growths, and necked crystals are described from zircon populations from granitic gneisses from the Precambrian of SW. Greenland. From observations of the distribution of internal growth zones it is concluded that whereas twinning takes place early in the growth history of elbow twins it can occur at any time during crystallization of the zircon. Parallel growth is attributed to a process of synneusis or attachment of zircons that have initially undergone separate growth histories. This implies that viscosity conditions of the rocks were low enough to permit the movement and collision of growing zircon crystals. The common occurrence of zircons with central constrictions, sometimes superimposed on transverse fractures, in zircon suites from the granitic gneisses is explained in terms of late-stage chemical corrosion accompanied by brittle fracturing.

Chemical and mineralogical investigations show that the Bitburg meteorite is not a pallasite, but a group-IB iron meteorite. Like other members of this group it contains chondritic silicates.

High-iron bustamite and apatite occur as subhedral large crystals up to 1 to 2 cm wide and 10 cm long in close association with spessartine in the disseminated sphalerite- and galena-bearing diopside-roepperite-calcite skarn at the New Broken Hill Consolidated mine (N.B.H.S.), New South Wales, Australia. Complete chemical analyses of the minerals have been made, together with physical, optical, and X-ray studies.