ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Brittle, Conchoidal
Brittle, UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
ZrO 2Arthur Thomas , Gemstones (2009)
(Mg,Fe)Al 3(BO 4)(SiO 4)OUlrich Henn and Claudio C.