ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
Conchoidal, Brittle, Conchoidal
SiO 2 + H 2OUlrich Henn and Claudio C.
AlO(OH)Walter Schumann , Gemstones of the world (2001) More from other references