ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Irregular, Irregular, Gemstones of the world (2001)
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001)
CaCO 3Ulrich Henn and Claudio C.