Conchoidal, ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle
Uneven, Uneven, ConchoidalArthur Thomas, Gemstones (2009)
SiCArthur Thomas , Gemstones (2009)
Na 4AlBeSi 4O 12ClMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references