1911 Encyclopædia Britannica/Danburite
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 3.0. 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.