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