ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
Conchoidal, Conchoidal, Gemstones of the world (2001)
Be 2BO 3(OH)Ulrich Henn and Claudio C.
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001)