Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
Gemstones of the world (2001), Difficult, Splintery
ThCa 2Si 8O 20Walter Schumann , Gemstones of the world (2001) More from other references
Nephrite: Ca2(Mg,Fe)5Si8O22(OH)2 Jadeite: NaAlSi2O6