| Alloclasite | |
| Imasymbol: | All |
| Color: | Steel gray to silver |
| Fracture: | Irregular/Uneven, Sub-Conchoidal |
| Mohs: | 5 |
| Luster: | Metallic |
| Streak: | Nearly black |
| Diaphaneity: | Opaque |
| Gravity: | 5.95 |
Alloclasite, or, is a sulfosalt mineral (IMA symbol: Acl).[1] It is a member of the arsenopyrite group. Alloclasite crystallizes in the monoclinic system and typically forms as columnar to radiating acicular prismatic clusters. It is an opaque steel-gray to silver-white, with a metallic luster and a black streak. It is brittle with perfect cleavage, a Mohs hardness of 5 and a specific gravity of 5.91–5.95.[2]
It was first described in 1866 for an occurrence in Romania.[3] Its name is derived from Greek for "other" and "to break," in reference to its distinct cleavage which distinguished it from the similar appearing mineral marcasite.[4] [2]
The mineral is monoclinic in the P21 space group.[5]