Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Brittle, Conchoidal
ThCa 2Si 8O 20Walter Schumann , Gemstones of the world (2001) More from other references
ZrO 2Arthur Thomas , Gemstones (2009)