Conchoidal, Conchoidal, Gemstones of the world (2001) More from other references
UnevenArthur Thomas, Gemstones (2009) Tough, UnevenArthur Thomas, Gemstones (2009) Tough, Brittle, Uneven
SiO 2 · nH 2OGemdat.org , Management Team (2012)
Mn 8Si 6O 15(OH,Cl) 10Ulrich Henn and Claudio C.