Sodalite

Sodalite is a feldspar-like zeolite mineral. It was the first discovered member of the sodalite mineral group, which also includes lazurite. Sodalite is used as a gemstone for its dark blue colour.

 Structure 
Like other zeolites, sodalite has a cage-like crystal structure. Sodalite's "cages" contain mostly sodium and chlorine.

 Sources 

Category:Tectosilicates
Category:Gemstones