Conchoidal, Conchoidal, Gemstones of the world (2001) More from other references, Brittle
Uneven, Uneven, ConchoidalAnthony et al, Handbook of mineralogy (2001)
SiO2 · nH2O
(Zn,Mn2+ ,Fe2+ )(Fe3+ ,Mn3+ ) 2O 4Anthony et al , Handbook of mineralogy (2001)