The results of reconnaissance melting experiments on Tertiary granophyres and Torridonian arkose at 1000 kg/cm2 water-vapour pressure show that the melting behaviour of these rocks can be viewed in relation to the synthetic system NaAlSi3O8-KAlSi3O8-SiO2-H2O. By analogy with this system, P-T curves are constructed for Skye granophyres and, viewed in relation to the stability of tridymite, the depth and temperature of emplacement are estimated. Further estimates of the likely depth of magma generation, and the behaviour of the country rocks at that level, lead to the conclusion that most of the Tertiary granitic rocks were produced through partial melting of Lewisian basement rocks, the heat being provided by the basic magmas available during this volcanic episode. Subsidiary amounts of granitic magma were similarly derived from higher levels, within the Torridonian arkose group, and evidence is provided for the depth and temperature at which these, together with tridymite-bearing metamorphosed arkose in Rhum, were produced.

Single crystal X-ray examination has shown that högbomite forms a series of polytypes, designated nH or nR, with hexagonal or rhombohedral lattices and hexagonal unit-cell dimensions a 5·72 Å, c 4·6 × n Å. The polytypes arise by variation, in a manner as yet undetermined, of the stacking sequence of approximately close-packed oxygen layers with interstitial cations on fourfold and on sixfold sites; the composition of 1/nth of a unit-cell may be represented as R2+1.0_1.6T4+0.2-0.4R3+3.7-4.3O2-7.6-8.0(OH)-0-0.4,, where R2+ = Zn, Fe, Mg, and R2+ = Fe, Al. The polytypes so far observed are 4H, 5H, 6H, 15H, 15R, and 18R. Minerals structurally related to högbomite are nigerite (3H) and taaffeite (4H). A new occurrence of högbomite, polytype 5H, with composition Ti1·7Fe1·6Mg6·3Al18·8Si0·2O40, is described from a spinel-free paragenesis in a magnesian skarn at Mautia Hill, Tanganyika. Another new occurrence in an aluminous xenolith in the Cashel gabbro in Co. Galway, Ireland, is recorded. X-ray powder data are given for two of the polytypes.

The transformation was followed in Amelia albite powders by variation in 2θ131−2θ13̄1 with time under isothermal conditions at various temperatures in the range 920°–1080°C. The activation energy of about 74 kcal mole-1 is rather larger than that obtained for the ordering process in synthetic NaAlSi3O8 under hydrothermal conditions.

Eclogite occurring about 20 miles east of Queenstown, Tasmania, is the first example of this kind of rock to be described in detail from Australia. It has the chemical composition of a basic igneous rock and consists of garnet (A115.8Fe‴0.6Fe″10.0Mg7.3Ca5.7Si24O96) and pyroxene (Ca4.5Na2.5Mg3.7Fe″0.7Fe‴0.4Ti0.1Aliv3.7Aliv0.7Si15.3O48)with amphibole, muscovite, zoisite, quartz, rutile, and pyrite. The eclogite consists of lenticular bodies within Precambrian garnetiferous schists.

The central region of a type 1 stone was found by optical and X-ray topographic examination to be densely populated with small inclusions. The X-ray studies indicated that these were precipitates formed after growth of the stone. Precipitate sizes fell into two groups, 1 µ or less, and around 5 µ. Many cases of decoration of grown-in dislocations by these precipitates were observed.

Brushite occurs as radial-concentric layers of prismatic crystals deposited on baked pellets of bentonite impregnated with cobalt oxide, placed in the reticulo-rumen of lambs as a preventive of cobalt-deficiency diseases. Collophane-like whitlockite, apparently pseudormorphous after brushite, occurs underneath the brushite layers, and struvite is found as rare minute crystals between the whitlockite and brnshite layers. Analytical and physical data are given for the first two minerals and the origin of the deposit is discussed.

By measuring the integrated line intensity on a Philips' X-ray diffractometer in place of the peak intensity and by paying due regard to the ease with which aragonite converts to calcite during cleaning and grinding operations, the proportion of calcite and aragonite in a pure calcium carbonate shell can be determined to within 1% of the total in less than 30 minutes.