ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
UnevenAnthony et al, Handbook of mineralogy (2001) More from other references, UnevenAnthony et al, Handbook of mineralogy (2001) More from other references, Brittle, Metallic
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)
CoAsSAnthony et al , Handbook of mineralogy (2001)