Conchoidal, ConchoidalAnthony et al, Handbook of mineralogy (2001), Brittle
Uneven-Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001)
SiCArthur Thomas , Gemstones (2009)
The chief constituent Lapis Lazuli is Lazurite, with the following chemical formula: (Na,Ca)8Al6Si6O24(S,SO)4