Rosasite and aurichalcite occur with other copper, zinc, and also lead minerals in Masson Cavern, Rutland Cavern, and other workings in the Heights of Abraham, Matloek Bath, Derbyshire. Partial analyses of two specimens each of rosasite and aurichalcite show Cu : Zn ratios typical of the respective species. They appear to have been formed by the action of solutions containing zinc on disseminated chalcopyrite. The infra-red absorption spectra of malachite, rosasite, aurichalcite, and hydrozincite, examined by the mull technique, are shown to fall into two groups corresponding with the structural groups established by X-ray work. Twin absorption maxima at O-H stretching frequencies are present in the spectra of malachite and of rosasite.

Epididymite, determined by means of its optical properties, X-ray powder pattern, and spectrographic analysis, was found in a desilicated pegmatite near Věžná, Western Moravia, Czechoslovakia. It was formed contemporaneously with minor amounts of milarite in a late hydrothermal stage by the action of sodium-rich solutions on beryl. This is the first occurrence of epididymite and milarite as alteration products of beryl and the first findings of epididymite in any other paragenesis than that of alkaline pegmatites. The optical properties of epididymite are re-examined and older data rejected.

A new occurrence of the tantalum minerals simpsonite and stibiotantalite is described from a lithium pegmatite at Mtoko, Southern Rhodesia. Optical, chemical, and powder X-ray data are given and the formula of simpsonite is considered; a new formula is proposed.

Chrysotile fibres, and also single crystals of lizardite, were dehydrated hydrothermally, and the resulting pseudomorphs studied by X-ray rotation photographs. The initial products are normally forsterite and disordered material; talc forms more slowly. At water pressures up to 600 kg/cm2, both forsterite and talc show strong preferred orientation. At higher pressures the talc is oriented but the forsterite tends to be unoriented. The orientation of forsterite formed at 550° C and 500 kg/cm2 differs from that found when chrysotile is dehydrated by heating in air. The orientation relationships suggest that, in the dry reaction, the forsterite orientation is controlled mainly by the octahedral layers of the chrysotile, while in the hydrothermal reaction it is controlled mainly by the tetrahedral layers. This does not support the generally accepted mechanism for the dry reaction. New mechanisms are suggested, for both dry and hydrothermal reactions, similar to that already suggested by us for the dehydration of brucite. The formation of talc in the hydrothermal reaction, and of enstatite in the dry reaction above 1000°, are also discussed. The dehydration of talc, to give enstatite, has also been studied using single crystals, and the mechanism of this process is briefly discussed.

Chemical analyses, optical data, and cell parameters are given for olivine (Fo90·3 and Fo91·4), orthopyroxene (Ca1·5Mg89·0Fe9·5 and Ca9·8Mg88·6Fe10·6), clinopyroxene (Ca39·6Mg55·8Fe4·6), and chromian spinel from olivine nodules from the Carboniferous basalt of Calton Hill, Derbyshire. Chemical and modal analyses of the nodules and of their host rock are also presented. The distribution of Mg and Fe in the coexisting pyroxenes is fairly similar to that observed by Ross, Foster, and Myers (1954) but differs slightly in that the extension of the pyroxene tie-line intersects the Ca-Mg side of the Ca-Mg-Fe triangle. The clinopyroxene is a normal augite rather than the hydrous augite previously reported (Tomkeieff, 1928). The high chromium content of the spinel and clinopyroxene contrasts with the low value for this element in the host rock, suggesting that these minerals are not differentiates of the basaltic magma: the nodules are considered to represent fragments from a deep-seated peridotite.

Chemical, optical, and X-ray data are presented on three analcimes from a differentiation sequence, olivine-theralite to analcime-tinguaite; compared with the ideal analcime composition, they reveal replacement of NaAl→Si. Optical and X-ray data on these minerals accord reasonably well with analcimes possessing similar compositions, and synthesized in the sub-solidus region in the NaAlSiO4-NaAlSi3O8-H2O system.

The mineral woodruffite, which has so far been reported from only one locality, Sterling Hill, New Jersey, has been found to occur in the Sandur area. Its physical and chemical characters are given. Indexing of the X-ray powder photograph shows that the mineral is most probably tetragonal with a 8·42, c 9·28 Å.

Mineralogic data on a chrome garnet, a spessartine, and a spandite from India are presented. The chrome garnet, named hanléite by Fermor, carries 89·7 % uvarovite, and is not a distinct mineral. The end-member compositions of the manganese garnets, recast from their chemical analyses, lend support to the existence of calderite and blythite as garnet end-members.

The suitability of monochromators for visual applications in petrographic mineralogy is discussed, and a new and inexpensive instrument employing a graded interference filter is described.

A simple form of adjustable monochromatic interference filter, suitable for both transmitted- and reflected-light microscopy, is described and figured.