Forsterite formed from serpentine powders at various temperatures up to 800° C has been measured quantitatively by X-ray diffraction. The results are considered in relation to a reaction mechanism proposed by Ball and Taylor and are shown to be inconsistent with the details of this mechanism. An alternative mechanism is proposed by which all or nearly all the Mg ions together with some of the Si ions liberated in the reaction zones where water is formed migrate into regions where forsterite is formed. This mechanism is in closer accord with the experimental results. The retarded development of enstatite until temperatures above 1000° C are used is attributed to the nature of the reaction by which it is formed, namely a reaction between forsterite and silica.

The Ceylonese gemstone sinhalite, AlMgBO4, is isomorphous with olivine and chrysoberyl. Aluminium and magnesium are oetahedrally coordinated and boron occupies slightly distorted tetrahedra. Because of size differences, the smaller Al ion can be assigned to the inversion symmetry sites, with Mg in mirror plane positions. Least-squares refinement based on single crystal X-ray data gave an accurate set of atomic coordinates with mean interatomic distances: Al-O 1·90, Mg-O 2·10, B-O 1·49 Å.

An accurate and highly sensitive method for the measurement of reflectivities incorporating a photomultiplier and a direct-reading galvanometer is described. The high sensitivity of the technique permits the determination of spectral reflectivities as opposed to ‘white’ light reflectivities, the latter values being subject to variation according to the type of apparatus used in their determination. The absolute spectral reflectivities of pyrite determined by the method are in good agreement with those quoted by some previous workers. Spectral reflectivities in air and oil and refractive and absorption indices are given for wavelengths from 430–650 mµ for manganese oxide minerals.

In an attempt to assemble together the sparse information regarding the eighty meteorites recorded as having fallen in Italy, tables have been prepared dealing respectively with chronology, name and generalities, synonymy, and literature, together with a distribution map. They are intended not only to help correct identification of pieces widespread in museums or private collections, but also to begin a labelling unification process, in order to avoid confusion arising from a wide variety of synonyms.