A mineral neosilicate, composition CaBSiO₄(OH), crystallising in the monoclinic system. It usually occurs in crystals showing many faces and having an equidimensional habit. It may also be fine granular or compact and massive. Hardness is 5–5½ on Mohs scale; specific gravity is 2.8–3.0. The lustre is vitreous, the crystals colourless or white with a greenish tinge. Datolite is a secondary mineral found in cracks and cavities in basaltic lavas or similar rocks associated with zeolites, apophyllite, prehnite, and calcite. It is found in the Harz Mountains, Germany; Bologna, Italy; and Arendal, Norway. In the United States fine crystals have come from Westfield, Massachusetts; Bergen Hill, New Jersey; and various places in Connecticut. In Michigan, in the Lake Superior copper district, datolite occurs in fine-grained porcelainlike masses which may be coppery red because of inclusions of native copper.