Conchoidal, Conchoidal, Gemstones of the world (2001)
Uneven, Uneven, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Conchoidal, Brittle
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001)
Fe 2O 3Arthur Thomas , Gemstones (2009)