Societies and Academies

Abstract

LONDON. Mineralogical Society, June 13.—Prof. W. J. Lewis, F.R.S., president, in the chair.—G. S. Blake: Zirkelite from Ceylon. The results of five analyses made on fragments grouped together according to their specific gravity, which ranged from 5.2 to 4.4, showed remarkable variation in the percentage composition, the densest containing about 20 per cent, thoria and little uranium, and the lightest 14 per cent. U3O8 and little thorium; the precise formula is uncertain. A few crystals, some simple and some twinned, were met with; they apparently belong to the hexagonal system (cr=53° 22′), the observed forms being c(0001), m(1010), r(1011), s(2021), d(1012), e(2023), and r the plane of twinning; they were opaque in mass, but translucent and isotropic in splinters.—Rev. Mark Fletcher: Note on some crystals of artificial gypsum. The crystals, which were formed in the condensing plant of a distillery at Burton-on-Trent, were twinned about 101, and the forms 100, no, 230, in were observed.—L. J. Spencer: The larger diamonds of South Africa. Historical notes relative to the “Excelsior,” “Jubilee” and “Imperial” diamonds were given, together with a tabular statement of the weights of the rough and cut stones in carats and grams, and the percentage yield of the cut brilliants from the rough.—F. H. Butler: Breccia-tion in mineral veins. In vein-breccias due to fracture in situ (crush-breccias) replacement of country-rock is a characteristic feature. Where the coarse fragments in a brecciated fissure-vein indicate erosion, removal of fine rock debris may be inferred. Fragments that are angular and uneroded and completely isolated by encrusting material often indicate by shape and position their former existence as a single mass. The quiet removal of such fragments into a vein-cavity after reunion, and also the banding, with concomitant contortion of adjoining soft country-rock, by their cement-substance, may be ascribed to the hydrostatic pressure and the solvent and mineralising properties of the waters which furnished that substance. The coarse constituents of breccia may have been crushed in situ, or forced from fissure-walls by earth movements, or detached therefrom by aqueous pressure and solution.— Arthur Russell: Prehnite from the Lizard district. Two distinct types of crystals, tabular and prismatic, were recently found by the author on hornblende-schist at Pare Bean Cove, Mullion, Cornwall, the former showing the forms ooi, 302, 061, and the latter 100, 001, 110, 061, and the rare form 301.