Uneven, Brittle, Metallic, Gemstones (2009)
Conchoidal, Conchoidal, Gemstones of the world (2001)
Na 2[Al 2Si 3O 10] · 2H 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001) More from other references