ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Splintery, Brittle, Uneven
SiO 2Ulrich Henn and Claudio C.
NaCa 2(Mg 4Al)Si 6Al 2O 22(OH) 2Michael OâDonoghue , Gems, Sixth Edition (2006)