UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009)
Conchoidal, Splintery, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle
NaCa 2Al 5Si 5O 20 · 6H 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references
AlPO4 · 2(H2O)