Uneven, Uneven, Gemstones of the world (2001) More from other references
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
H 4Mg 3Si 2O 9Walter Schumann , Gemstones of the world (2001) More from other references
Be 3Al 2Si 6O 18Ulrich Henn and Claudio C.