Uneven-Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001)
Conchoidal, Conchoidal, Gemstones of the world (2001) More from other references, Brittle
The chief constituent Lapis Lazuli is Lazurite, with the following chemical formula: (Na,Ca)8Al6Si6O24(S,SO)4
SiO2 · nH2O