Ceruleite

Ceruleite comes from the Latin Caeruleus, for “sky-blue”, and this specific Ceruleite comes to us from Chile. Its hardness is 5-6 and its specific gravity is around 2.7. With only 20 known localities where this can be found worldwide, this specimen is quite rare. It really only occurs in oxidized arsenic-rich polymetallic deposits, so it’s not found everywhere. There’s no Wikipedia page for this rare mineral, and little more is known about it, but it’s quite a cool rock!