Gemstones of the world (2001)
Uneven, Subconchoidal, ConchoidalArthur Thomas, Gemstones (2009), Uneven, Subconchoidal, Brittle, Metallic, Brittle, Metallic
SiO 2Walter Schumann , Gemstones of the world (2001)
Zn 2(AsO 4)(OH)Michael OâDonoghue , Gems, Sixth edition (2006)