Uneven, Uneven, ConchoidalAnthony et al, Handbook of mineralogy (2001)
Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
(Ca,Mn2+ ,Fe2+ ) 3Al 2BSi 4O 15(OH)Anthony et al , Handbook of mineralogy (2001)
ThCa 2Si 8O 20Walter Schumann , Gemstones of the world (2001) More from other references