Cornwallite
Mineral Cu5(AsO4)2(OH)4
Take care.
- Contains arsenic: Wash your hands after handling it, don't make dust, and never heat it.
About it
Dark green crusts and tiny crystals of copper arsenate, often with olivenite, named for Cornwall where it was first found. Easily confused with pseudomalachite, its phosphate look-alike.
- Type
- Mineral
- Group
- Arsenate
- Formula
- Cu5(AsO4)2(OH)4
- Hardness (Mohs)
- 4.5
- Streak
- pale green
- Lustre
- vitreous (glassy), resinous
- Crystal system
- Monoclinic
- Colours
- dark green, blackish green, emerald green
- Transparency
- translucent
- Cleavage and fracture
- none; conchoidal fracture
Typical values: real specimens vary. For more, see mindat.org.