The hackmanite is a variety of Sodalite where the sulfur was substituted by the chlorine.
Placed in the darkness, this stone becomes almost white. In the light, it finds its purple color. The phenomenon is reversible. The name of this property is the "ténébrescence".
The hackmanites first ones of quality gemstone were discovered in Quebec.
To know more about the mineralogy of the hackmanite, see Mindat.org->
