Brittle, UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
Subconchoidal, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
(Mg,Fe)Al 3(BO 4)(SiO 4)OUlrich Henn and Claudio C.
(Fe,Mg,Zn) 2Al 9(Si,Al) 4O 22(OH) 2Ulrich Henn and Claudio C.