The color of rock salt—A review

✍ Scribed by Peter Sonnenfeld

• Book ID: 103360223
• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 1022 KB
• Volume: 94
• Category: Article
• ISSN: 0037-0738
• DOI: 10.1016/0037-0738(94)00093-a

✦ Synopsis

Pure rock salt is colorless, but natural occurrences are often discolored.

Halite may be discolored by: (a) the inclusion of interstitial matter; (b) impurities; or (c) structural defects in the crystal lattice.

Blue halite is absent beneath all potash seams and may occur some small distance above sylvite, but not above carnallite zones. It is frequently found in tectonically disturbed zones, in breached anticlines, fault zones, or fracture and crevice fillings.

It is easy to induce a blue color in the laboratory by: (a) various methods of irradiation;

(b) a soaking in sodium vapors; or (c) the emplacement of various impurities. None of these methods seems to have occurred in nature. Natural blue discoloration is concentrated in oviform clumps along paths of circulating brines. Descending brines quickly saturate with sodium and chlorine, leach, brecciate and recrystallize the halites and preferentially dislodge bromine ions from crystal lattices. Platelets of metallic sodium left behind in lattice defects cause a blue (or rarer yellow) discoloration.