ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Brittle, UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
SiO 2Ulrich Henn and Claudio C.
(Mg,Fe)Al 3(BO 4)(SiO 4)OUlrich Henn and Claudio C.