Conchoidal, Conchoidal, Gemstones of the world (2001)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Brittle, Conchoidal
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001) More from other references
ZrO 2Arthur Thomas , Gemstones (2009)