Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
Brittle, Metallic, Brittle, Metallic
ThCa 2Si 8O 20Walter Schumann , Gemstones of the world (2001) More from other references
Be 4Si 2O 7(OH) 2Anthony et al , Handbook of mineralogy (2001)