Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Metallic
Al 6B 5O 15(F,OH) 3Ulrich Henn and Claudio C.
Ca 2B 6O 11 · 5H 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references