Splintery, Brittle, Uneven
UnevenArthur Thomas, Gemstones (2009) Tough, UnevenArthur Thomas, Gemstones (2009) Tough, Brittle, Uneven
NaCa 2(Mg 4Al)Si 6Al 2O 22(OH) 2Michael OâDonoghue , Gems, Sixth Edition (2006)
Mn 8Si 6O 15(OH,Cl) 10Ulrich Henn and Claudio C.