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