Cuttings from their Eskdale no. 2 boring, Aislaby, near Whitby, at a depth of 4095–4100 feet from the surface were presented to the Geological Museum by the D'Arcy Exploration Co. Limited, in response to a request for a specimen from the Permian Saliferous Series which might contain polyhalite, a mineral already recorded by Professor C. E. Tilley from this boring (Min. Mag., 1943, vol. 26, p. lvii). The cuttings were examined by Dr. J. Phemister who found no polyhalite in them, but a small quantity of a mineral which he thought was probably boracite. In response to a request for additional material the company very kindly supplied further cuttings from depths in the bore between 4090 and 4160 feet.

Cristobalite is found as the first product in the conversion of quartz following a high-temperature heating, and it constitutes a large percentage of the crystalline material in most manufactured silica bricks. It is present also in fireclay products, the amount being dependent upon the nature of the raw material and the conditions of firing. In the majority of these products the cristobalite is only poorly developed, i.e. the crystals are only perfect over distances of the order of about 1 × 10-6 cm. This value is derived from the diffuseness of the high-order reflections on the X-ray powder photograph. On the other hand, the crystals of cristobalite are well developed in the hot face of an open hearth silica roof-brick.

During the course of a study of the interaction of certain pure refractory oxides at high temperatures it became necessary to obtain accurate values for the lattice parameters of α-alumina and chromic oxide. Values obtained by previous workers, listed in table I, did not attain a greater accuracy than one part in 2000, whereas the use of large-diameter powder cameras calibrated with quartz now yield lattice parameters accurate to at least one part in 30,000.

Samples of the calcined oxides were examined in a 19 cm. diameter powder camera, alumina with cobalt Kα radiation and chromic oxide with chromium Kα radiation. Results are given in tables II and III.

Unpublished work carried out in this laboratory several years ago had shown that the first-order basal X-ray reflections of illite from South Wales occurred at a spacing of about 10Å both with potassium- and calcium-saturated samples. Recently Jackson and others observed that hydrated mica samples having a 10Å basal spacing when saturated with potassium, showed a 12 to 13Å. spacing after saturation with calcium. They interpreted their results by ascribing to illite a limited capacity for reversible lattice shrinkage and expansion, identical in type with that known for montmorillonite.

In order to study the problem further three illite and two glauconite samples were treated with concentrated calcium chloride solutions for five weeks under frequent renewal of the solution.