Uneven, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Even
Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
Perfect {010} imperfect {100}
On {10 1 0}, perfect; parting on {000 1 }
Ca2Al3(SiO4)3(OH)
(Zn,Mn2+ )OMichael OâDonoghue , Gems, Sixth Edition (2006)