Uneven, Uneven, ConchoidalAnthony et al, Handbook of mineralogy (2001)
Micaceous, Brittle
(Ca,Mn2+ ,Fe2+ ) 3Al 2BSi 4O 15(OH)Anthony et al , Handbook of mineralogy (2001)
KAl 2AlSi 3O 10(OH) 2Walter Schumann , Gemstones of the world (2001) More from other references