A rare mineral consisting of a sulphide and arsenide of iron and cobalt (often with other metals), typically occurring as aggregates of slender, steel-grey crystals.
Approximate formula: (Co,Fe)AsS. Crystal system: orthorhombic.
Mid 19th century; earliest use found in James Dana (1813–1895), geologist, zoologist, and teacher. From German Alloklas alloclase + -ite.