Uneven, Subconchoidal, Uneven, Subconchoidal, Splintery, UnevenArthur Thomas, Gemstones (2009)
Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
Al 2SiO 5Michael OâDonoghue , Gems, Sixth edition (2006) More from other references
Al 6B 5O 15(F,OH) 3Ulrich Henn and Claudio C.