A new copper arsenate, dimorphous with cornwallite, has been found on specimens from five localities in Cornwall, one in Devon, and one in Cumberland. The name cornubite (from Cornubia, the medieval Latin name for Cornwall) is proposed for the new mineral. Chemical analyses of cornubite and cornwallite agree well with Cu5(AsO4)2(OH)4; sp. gr. cornubite 4·64, cornwallite 4·52. X-ray study suggests that the unit-cell of cornubite has a volume of 228 Å.3 or a simple multiple thereof. New X-ray data for cornwallite (a 17·33, b 5·82, c 4·60 Å., β 92° 13′) agree well with L. G. Berry's except for a. Powder data for both are given.

The complex kalsilite-bearing melilite-nephelinite from Mt. Shaheru in the Belgian Congo with götzenite, combeite, and kirschsteinite contains yet another new silicate for which the name delhayelite is proposed.

Delhayelite is orthorhombic with a 6·53, b 24·65, c 7·04 Å. Possible space-groups Pmn21 and Pmmn. Weak super-cell with doubled a-axis. Distinct cleavage parallel to (010). Birefringence weak. α ≈ β ≈ γ = 1·532. 2Vα = 83°. Optical orientation: a = α, b = γ, c = β. Sp. gr. 2·60. Chemical composition corresponds to the tentative formula (Na,K)4Ca5Al6Si32O80.18H2O.3(Na2,K2)(Cl2,F2,SO4).

A hydrated barium-strontium pyrochlore with only subordinate amounts of Ca and Na has been found in a weathered biotite rock (contact-rock of a carbonatite) from Panda Hill, Tanganyika, as small euhedral yellowish-grey cubic crystals (showing the combination of the octahedron and the cube) in a rock containing euhedral biotite, some orthoclase, and several other minerals. Hydrated Ba-Sr pyrochlore is isotropic, the refractive index varies from 2·07 to 2·10. The reflectivity (vertical illumination) is 13·2 %. H. Poor {111} cleavage. The pyrochlore structure (space-group O7h–Fd3m) and the unit-cell dimensions (a 10·562 Å.) are derived from X-ray powder and Weissenberg photographs. The calculated specific gravity is 4·01 (observed, 4·00 on dried material). Chemical analysis gives BaO 12·5, SrO 6·4, Na2O 0·28, K2O 0·25, CaO 1·35, rare earths (mainly Ce2O3) 2, ThO2 0·6, FeO 0·45, TiO2 3·9, Nb2O5 67·0, Ta2O5 0·22, H2O+ 4·0, other constituents 2·21, total 101·16. After deduction for impurities the following formula resulted: (Ba0·30Sr0·22Ca0·05Ce0·04Na0·03Fe0·02K0·01Th0·01)(Nb1·83Ta0·004Ti0·17)O5·61(H2O)0·80.

The ideal formula for pyrochlore is A2B2O6(F,OH). In the mineral described only a third of the A-positions are occupied by Ba, Sr, etc. Infra-red spectrophotometry does not indicate hydroxyl-groups. When the mineral is treated with TINO3 solution the intensities of the X-ray diffraction lines 333/511, and 444 are changed; hydrated Ba-Sr pyrochlore shows a certain exchange-capacity.

The name pandaite, from Panda Hill, is proposed for the new mineral.

Veins and nodules of cornstone, enclosed in sandstone, have reacted to the thermal influence of a Tertiary dolerite dyke by the development of a wollastonite reaction skarn. This can be shown to have formed as a result of pseudomorphous replacement of the quartz grains by wollastonite, due to outward diffusion of calcium. The process is believed to have taken place at the inversion temperature of quartz (573° C.).

Samples of magnetite containing exsolution bodies of ilmenite, or of ulvöspinel and ilmenite, were heated at 1,250–1,300° C. under oxidizing and under reducing conditions.

In the former case, the product consisted of magnetite, ferri-ilmenite, and pseudobrookite. In the latter, loss of oxygen converted a magnetite-ilmenite intergrowth into a homogeneous Fe3O4-Fe2TiO4 spinel solid solution, while a magnetite sample originally carrying ulvöspinel in addition to ilmenite yielded a spinel phase with surprisingly low cell dimension, together with some metallic iron.

Infra-red absorption spectroscopy has been used to study the retention of hydroxyl groups by kaolinite and halloysite after heat treatment in the range 600° C. to 850° C. Structurally disordered specimens initially lose water more rapidly than do ordered specimens, but retain hydroxyl groups at higher temperatures. Work on the phases obtained above 1100° C. is incomplete, but results for the lower temperatures indicate that the ordered structures tend to retain their atomic arrangement and form metakaolin, whereas disordered structures readily rearrange to yield γ-alumina, to the formation of which water is probably essential.

The water vapour released upon heating the specimen is driven through a water absorber. The intensity of the exothermic reaction produced by absorption of the water is recorded against the temperature of the specimen. A series of curves obtained with various clay minerals are presented to illustrate the method. The significance of results in the identification of the clay minerals and the determination of their structure is considered.

The observed order of importance of the forms of baryte, anglesite, and celestine is first determined by a modification of the methods used by Donnay and Harker. Their hypothesis is applied to determine the space-groups of these minerals by morphological means, and a comparison is made of the observed and theoretical orders of importance of forms in these minerals. It is concluded that agreement is poor between the observed and predicted frequencies of forms in the baryte group. The rank distribution of some of the more important forms is presented graphically.

A new occurrence of helvine, the rare manganese end-member of the helvine group, is described. The mineral is found in a granite pegmatite associated with microcline-perthite, petalite, spodumene, muscovite, and spessartine. A chemical analysis of the mineral is given.