Member of the nesosilicates (chain silicates) CaSiO₃ and associated with the pyroxenes, although it does not possess a pyroxene atomic lattice and is termed a pyroxenoid (along with pectolite (Ca₂NaH[SiO₃]₃) and rhodonite); sp. gr. 2.8–3.1; hardness 4.5–5.0; triclinic; white to grey; vitreous to pearly lustre; crystals tabular, prismatic, also occurs massive and cleavable, or fibrous; cleavage perfect {100}; occurs in metamorphosed, silicaceous limestones, and alkaline, igneous rocks, and associated with calcite, epidote, and tremolite; soluble in hydrochloric acid with the separation of silica. It is used as a source mineral for rock wool of high strength and with long fibres, and is named after the British chemist and mineralogist William Hyde Wollaston (1766–1828).