DANBURITE  , a rare

mineral species consisting of calcium and boron orthosilicate, CaB2(SiO4)2, crystallizing in the orthorhombic system . It was discovered by C . -U . Shepard in 1839 at Danbury, Connecticut, U.S.A., and named by him after this locality . The crystals are prismatic in habit, and closely resemble topaz in form and interfacial angles . There is an imperfect cleavage parallel to the basal plane . Crystals are transparent to translucent, and colourless to pale yellow; hardness 7; specific gravity 3•o . At Danbury the mineral occurs with microcline and oligoclase embedded in dolomite . Large crystals, reaching 4 in. in length, have been found with calcite in veins traversing granite at Russell in St Lawrence county, New York . Smaller but well-developed crystals have been found on gneiss at Mt . Scopi and Petersthal (the valley of the Vals Rhine) in Switzerland . Splendid crystals have recently been obtained from Japan .