UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Conchoidal
Brittle, Metallic, Brittle, Metallic
Ca 2B 5SiO 9(OH) 5Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Be 4Si 2O 7(OH) 2Anthony et al , Handbook of mineralogy (2001)