UnevenWalter Schumann, Gemstones of the world (2001) More from other references, UnevenWalter Schumann, Gemstones of the world (2001) More from other references, Uneven
Conchoidal, Conchoidal, Gemstones of the world (2001) More from other references, Brittle
(Zn,Fe)SMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references
SiO2 · nH2O