Uneven, Uneven, Gemstones of the world (2001) More from other references
ConchoidalArthur Thomas, Conchoidal, Brittle
H 4Mg 3Si 2O 9Walter Schumann , Gemstones of the world (2001) More from other references
Mn 3Al 2(SiO 4) 3Arthur Thomas , Gemstones (2009)