Conchoidal, Conchoidal, Gemstones of the world (2001) More from other references, Fibrous
UnevenArthur Thomas, Gemstones (2009) Tough, UnevenArthur Thomas, Gemstones (2009) Tough, Brittle, Uneven
CaAl 2(Fe3+ ,Al)Si 3O 12(OH)Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Mn 8Si 6O 15(OH,Cl) 10Ulrich Henn and Claudio C.