DATOLITE, a mineral species consisting of basic calcium and boron orthosilicate, It is white or colourless, often with a greenish tinge, and may be either transparent or opaque; it usually occurs as well-developed monoclinic crystals bounded by numerous bright faces, many of which often have a more or less pentagonal outline, but also as masses with a granular to compact texture, the fractured surfaces having the appearance of porcelain when the mineral is compact. Hardness ; spe cific gravity 3•o.
Datolite is a mineral of secondary origin, and in its mode of occurrence it resembles the zeolites, being found with them in the amygdaloidal cavities of basic igneous rocks such as basalt ; it is also found in gneiss and serpentine, and in metalliferous veins and in beds of iron ore. At Arendal in Norway, the original locality for both the crystallized and botryoidal, or fibrous variety (known also as botryolite), it is found in a bed of magnetite. In amygdaloidal basaltic rocks it is found at Bishopton in Renfrew shire and near Edinburgh ; and as excellent crystallized specimens at several localities in the United States.