Conchoidal, Conchoidal, Gemstones of the world (2001) More from other references, Brittle
UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009)
SiO2 · nH2O
NaCa 2Al 5Si 5O 20 · 6H 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references