Conchoidal, Conchoidal, Gemstones of the world (2001)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001) More from other references
Be 3Al 2Si 6O 18Ulrich Henn and Claudio C.