Splintery, Brittle, Uneven
Uneven-Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001)
NaCa 2(Mg 4Al)Si 6Al 2O 22(OH) 2Michael OâDonoghue , Gems, Sixth Edition (2006)
The chief constituent Lapis Lazuli is Lazurite, with the following chemical formula: (Na,Ca)8Al6Si6O24(S,SO)4