Uneven, Uneven, Gemstones of the world (2001) More from other references
Brittle, UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
Ca 10Mg 2Al 4(SiO 4) 5(Si 2O 7) 2(OH) 4Ulrich Henn and Claudio C.
(Mg,Fe)Al 3(BO 4)(SiO 4)OUlrich Henn and Claudio C.