Fibrous, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references
Uneven-Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001)
AlAl6O3BSi3O18
The chief constituent Lapis Lazuli is Lazurite, with the following chemical formula: (Na,Ca)8Al6Si6O24(S,SO)4