These two minerals were described by Eakle from the crystalline limestone at Crestmore, Riverside County, California. Both were shown to be hydrated monocalcium silicates, containing small amounts of P2O5, SO3, and CO2, occurred with a fibrous habit, and had closely similar optical properties. They were distinguished chiefly by the higher water content (approx. 1.3 mol.) of crestmoreite as compared with riversideite (0.5 mol.), and by the fact that the former was included directly in the calcite, whereas the latter formed veins in masses of idocrase which were contained in it. The minerals had been produced under hydrothermal conditions caused by igneous intrusions. In both cases, the primary material was believed to have been wilkeite, which is an apatite mineral with much of the phosphorus replaced by sulphur, silicon, and possibly carbon.

As part of a study of the structure of whitlockite (β-Ca3(PO4)2) attempts were made to prepare single crystals of the mineral synthetically. At 1180° there is a polymorphic transition from the rhombohedral β-form to a high-temperature monoclinie form α-Ca3(PO4)2. The density of the α-form is 12% less than that of the β-form and large crystals were not found to transform without powdering. CaCl2 was therefore added as a flux to see whether crystals of Ca3(PO4)2 could be produced from a melt below 1180°. The melting point of pure Ca3(PO4)2 is about 1800°. In addition to chlorapatite (Ca5(PO4)3C1), a phase of composition Ca2PO4Cl was produced. This compound had been earlier observed by Cameron and McCaughey, who identified the crystals as being closely related to the mineral spodiosite (Ca2PO4F).

In a recent paper, Cole, Sörum, and Taylor described X-ray measurements on a number of plagioelases with compositions ranging from pure albite to pure anorthite. As a result, they were able to make more precise, and extend, the structural interpretations proposed on the basis of earlier X-ray investigations of the three typestructures, albite, anorthite, and intermediate plagioclases (Taylor, Darbyshire, and Strunz; Chao and Taylor). At the same time, new complexities were revealed which called for more detailed examination, among them the fact that the anorthite-type structure, with c-axis ∼14 Å., may have either a body-centred or a primitive unit cell. The body-centred cell was observed with a material containing 71.5% anorthite, the primitive cell with a nearly pure anorthite, but there was not sufficient evidence to show whether the difference was due entirely or largely to the difference in chemical composition, nor was a detailed investigation made of the effects of heat-treatments.

It has long been realized that grinding increases the cation-exchange capacity of minerals and that it damages their crystal structures. However, while a considerable amount of data has been accumulated with regard to the effect upon various minerals, and clay minerals in particular, very little is known about how micas behave and such results as are available are somewhat inconsistent (1, 2, 3). In view of this and of a fortuitous observation that short-period grindingin an agate mortar affected the nature of muscovite considerably, a more detailed study of this subject has been undertaken.

Numerous investigations of the effect of heat on minerals of the kaolinite group have established that these minerals are characterized by two major thermal reactions below 1000° C. An intense and abrupt endothermal reaction between 500 and 600° C. has been attributed to the loss of chemically combined water from the kaolinite structure. At about 980° C. these minerals experience an exothermal effect. The intensity and rapidity of this reaction indicate a crystallization process. Certain investigators have ascribed this reaction to the crystallization of gamma alumina (Insley and Ewell, 1935). Comeforo, Fischer, and Bradley (1948), on the other hand, have concluded that it represents crystallization into mullite nuclei of articulated units derived from the original material.

During a recent investigation of the hydrothermal mineralization associated with the Shap granite, nacrite was found in a quartz vein in the Shap Blue quarry. This quarry has been opened for roadstone in the metamorphosed Borrowdale lavas, 700 yards north of the granite contact on the west side of the Penrith-Kendal road, three miles south of Shap village. Further examination showed that nacrite often coats shear joints in fault breccias and shatter belts in the metamorphosed andesites. It is associated with chlorite, haematite, pyrite, and traces of erythrite, and often with later quartz, calcite, and baryte veins.

Nacrite from this locality occurs as microcrystalline aggregates on joint faces, usually only in thin layers but layers up to 5 mm. thick have been found.

Available information on the clay mineral saponite shows an amazing degree of variation and considerable discrepancies, probably due to investigation of impure samples. The clay mineral described in this paper was essentially pure and furthermore it seems to represent a magnesium end-member of the montmorillonite group.

Optical, chemical, X-ray, and differential thermal data of this particular saponite are presented, as well as data on some associated minerals, namely, a chlorite, two antigorites, and a chrysotile-asbestos.

The influence of Mg++, as the only natural occurring exchangeable base, on the nature of the X-ray diffraction and differential thermal diagrams leads to some interesting observations.