Blue Halite.
Remarkable deep blue and occasionally purple forms of halite (rock salt) have long been known. These occur associated with potassium minerals in the Zechstein basin of northern Germany, elsewhere in Europe, and in North America. In recent laboratory studies, data have been developed which confirm the hypothesis that this coloration in natural salt may be attributed to gamma-ray bombardment by associated potassium-40 from sylvite, accompanied or followed by structural deformation.
Howard
C L
CL
Kerr
P F
PF