Gems, Conchoidal, Brittle
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Ca 3Ti4+2(Fe3+2Si)O 12Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
SiO 2Ulrich Henn and Claudio C.