Uneven, Uneven, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Conchoidal, Brittle
Uneven, Uneven, ConchoidalGemdat.org, Management Team (2012)
Fe 2O 3Arthur Thomas , Gemstones (2009)
Mn 3Al 2(SiO 4) 3Arthur Thomas , Gemstones (2009)