The parageneses are given of ten new occurrences of carminite [PbFe2(AsO4)2(OH)2] and eleven of beudantite [PbFe3AsO4SO4(OH)6] in Cornwall and Cumberland, with an account of the alteration of carminite to beudantite and of beudantite to plumbojarosite or to beaverite.

An X-ray examination of the type specimen of stokesite gave a 14·41, b 11·61, c 5·23 Å.; space-group Pnna. The unit cell contains 4[CaSnSi3O11H4] and is derived from Hutchinson's morphological unit by the transformation [010/001/100]. X-ray powder data are given.

A kinetic analysis is presented of the data of MacKenzie (1957) on the hydrothermal treatment of NaAlSi3O8 under isobaric, isothermal conditions in the temperature range 450° C. to 1000° C.

The analysis indicates the existence of a smeared polymorphic transformation in the temperature range around 600° C. The activation energy for the transformation is about 60 kcal. mole−1 and has been equated with the process of self-diffusion involved in Al-Si ordering in the structure. Some dry-heating experiments and the influence of varying water vapour pressure are discussed.

Many specimens of plinthite, a species described from Co. Antrim by T. Thomson in 1836 and later from Skye by M. F. Heddle, prove to be mixtures of zeolites and hematite. Both original analyses are those of a ferruginous clay (a mixture of hematite, kaolinite, and montmorillonite). The type specimen (Thomson Collection) is a red clay in the montmorillonite group intimately mixed with hematite and a little analcime.

Experimental data in the system CaO-MgO-FeO-SiO2 suggest that there may be a plateau on the liquidus and solidus of the multicomponent system basalt-peridotite. If this is so, fusion of peridotite would produce only basaltie magmas over a wide temperature range; when the temperature reached a value such that the liquid crossed the threshold of the plateau, there would be a rapid increase in the amount of fusion for small temperature increases, with the formation of picritic magmas; basaltic magmas containing suspended forsteritic olivine crystals could dissolve them if the temperature rose slightly above that of the plateau threshold; a high proportion of a picritic magma would crystallize in a small temperature interval, with the precipitation of forsteritic olivine that was only slightly zoned. These possibilities are compared with current theories, and it is concluded that several petrological axioms may require critical re-examination. An experimental procedure is outlined to determine the shape of the liquidus and solidus in the basalt-peridotite system.

The problem of silicate immiscibility, of petrological and technological interest, is discussed in terms of the structures of silicate crystals and certain phase diagrams. Physical chemical principles are employed to indicate the author's basis for suspecting that certain structures in the crystalline solid are carried over into the melt and are a major contributory cause of silicate immiscibility. These structures appear to be limited to the neso (SiO4)4−, soro (Si2O7)6−, cyclo (Si3O9)6−, and ino (SiO3)2− types of silicate polymers and do not include the more complex phyllo- and tecto-silicate polymers.

Secondary minerals described from Tertiary amygdaloidal basalts in the Hunter Springs area, Barrington, New South Wales, are regarded as having been deposited from cold solutions some considerable time after consolidation of the basalts. The constituents in the solutions were evidently derived from the basalts by the action of circulating meteoric waters rather than by deuteric activity.

A method of quantitative analysis by photometry of X-ray powder diffraction patterns is described. Co-Kα radiation is used and absorption difficulties are overcome by using thin diluted specimens containing an internal standard. An arbitrary universal intensity scale has been established and the values for the stronger lines of a number of minerals are given. Within individual patterns these are consistent with published data obtained by counter diffractometry.