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.

Two occurrences of rutile are reported from Big Bell in Western Australia containing up to 5·8 wt % WO3, 1·7 wt % Sb2O5, and 1·7 wt % FeO. One occurs in a mica schist, and the other in a pegmatite, and both contain a fine intergrowth of ilmenite lamellae. Small grains of gudmundite are associated with the rutile in the pegmatite. Microprobe analyses do not conclusively establish the mechanism of isomorphous substitution.

The chemical analyses, structural formulae, and optical data of seven orthopyroxenes and six clinopyroxenes, all from the charnockite series of Amaravathi, are presented. The orthopyroxenes are in the hypersthene-ferrohypersthene range while the clinopyroxenes are in the sahlite range. The aluminous nature of the pyroxene is believed to be the result of high pressure. The clinopyroxenes have the granulite trend on the Wo-En-Fs plot. The tie-line projections and the KD values for the pyroxene pairs indicate conditions of chemical equilibrium around 670 °C for the charnockite series of Amaravathi.

Xenoliths of eucritic gabbros in an alpine-serpentinite body at Wairere have been altered to rodingites and xonotlite about their margins by hydrothermal metasomatism at temperatures between 430–470°C A chemical analysis and the optical properties of the xonotlite are reported, the textures of the rocks are described, and the metasomatic process is discussed.

Urea, a new mineral identical with the artificial compound, occurs as crystals associated with phosphammite, ammonian aphthitalite, and weddellite in guano from Toppin Hill, 123° 56′ E., 28° 42′ S., Western Australia. The urea occurs as elongated tetragonal pyramids, space group , a 5·646, c 4·701 Å, X-ray powder data are given. Optical properties: ω 1·484, ε 1·603. Chemical analysis gave urea, CO(NH2)2 96·0, H2O− 0·46, Na 0.13, K 0·35, Ca 0·07, Mg 0·03, S 0·11, P 0·24, NH3 < 1·0 %, remainder probably mainly H2O+; urea 96 %, impurities 4 %. Type material is preserved in the collection of the Government Chemical Laboratories, Perth, Western Australia.

Pale-blue cordierite (complete analysis given; shows total iron oxides only 0·98 %) occurs in phlogopite schist near White Well (24° 28′ 30″ S. 116° 2′ E.) 20 miles north-west of Yinnietharra, Western Australia. Associated minerals are corundum, dravite, and sillimanite, accessory zircon and rutile. The cordierite is in translucent masses to 8 ×8×4 cm with vitreous lustre, D 2·57, α 1.536, β 1·540, γ 1·543, all colourless, 2Vα80° Unit cell a 17·055, b 9·724, c 9·350 Å. The host phlogopite (complete analysis given) is in brown flakes to 1 cm, D 2·88, α 1·558, β 1·585, γ 1·59, 2Vα 5–20° 1 M polymorph.

Three generations of homogeneous titanomagnetite in a hawaiite from Saint-Clément may be defined by differences in size, habit, or reflectance, and are believed to correspond to different crystallization stages of the lava. Chemical compositions were determined by electron microprobe, and by X-ray and thermomagnetic methods.

Larger crystals are of intratelluric origin and occur either as inclusions in phenocrysts of early clinopyroxene (generation 1) or separately in the groundmass (generation 2); in the latter case, they always show evidence of resorption. Post-eruptive titanomagnetite (generation 3) is smaller and so highly oxidized that it is better termed titanomaghemite. Since the maghemitization, which is a low temperature process, alters the metallic ratios (especially the Fe/Ti ratio) the metallic contents at the time of the high-temperature crystallization are exactly known only for the intratelluric titanomagnetites.

As intratelluric crystallization proceeds Ti content increases greatly (5 to 14%); Mn also increases (but slightly), A1 and Mg decrease, while results for Cr are inconclusive. Apparently these changes go on until the post-eruptive crystallization stage.

The titanium trend is contrary to common belief. However, it is in accordance with predictions from the Fe-Ti-O system and may be explained by a decrease in oxygen fugacity during magma ascent.

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.

Silicate minerals show several correlations between structure type and elastic constants. Stiffness coefficients are generally larger in the direction of Si-O bonding. A simple mechanical analogy in which atomic bonds are simulated by springs connected in series and parallel is used to estimate the size and anisotropy of the elastic moduli and their pressure derivatives.

Heating experiments provide strong evidence that the transparent green coats on some diamonds from each of many localities are caused by α-particle irradiation after kimberlite injection and subsequent cooling. The natural diamonds with more or less homogeneous transparent green coats, studied in this work, appear to have received doses of at least 5 × 1013−1 × 1014 α.cm−2. For Pre-Cambrian kimberlites, such doses could occur if certain regions of the diatremes contained ⩾20 ppm by weight of equivalent uranium, after kimberlite injection and solidification.

Such considerations lead to the prediction that the radioelement concentrations in the Finsch kimberlite diatreme and the Bellsbank fissure kimberlite are considerably greater than those in the Premier mine, though radioelement segregation could produce the required local concentrations. Some exploratory autoradiographic measurements made on two kimberlite rock samples from Premier and De Beers Mines indicated that the radioelements were apparently distributed on a submicron scale, which would be a necessary, but not sufficient, condition for uniform α-irradiation of diamonds.

Diamonds from various alluvial sources showing green and brown spots arising from much heavier and more localized radiation damage are also discussed.

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.