Handbook of mineralogy (2001), Difficult, Fibrous
Uneven, Uneven, Gemstones of the world (2001) More from other references
Ca 6Si 6O 17(OH) 2Michael OâDonoghue , Gems, Sixth Edition (2006)
Ca 10Mg 2Al 4(SiO 4) 5(Si 2O 7) 2(OH) 4Ulrich Henn and Claudio C.