Halogen minerals

(mineralogy) Any of the naturally occurring compounds containing a halogen as the sole or principal anionic constituent.

Naturally occurring compounds containing a halogen as the sole or principal anionic constituent. There are over 70 such minerals, but only a few are common and can be grouped according to the following methods of formation.

1.Saline deposition by evaporation of seawater or salt lakes. Halite (rock salt), NaCl, is the most important of this type. Of the other minerals associated with halite, sylvite, KCI, andcarnallite, KMgCl₃·6H₂O, are the most important.

2.Hydrothermal deposition. Fluorite, CaF₂, is the chief representative of this type. Cryolite, Na₃AlF₆, may be of primary deposition or may result from the action of fluorine-bearing solutions on preexisting silicates. See also Cryolite; Fluorite.

3.Secondary alteration. Chlorides, iodides, or bromides of silver, copper, lead, or mercury may form as surface alterations of ore bodies carrying these metals. The most common are cerargyrite, AgCl, and atacamite, CU₂(OH)₃Cl. See also Cerargyrite.

4.Deposition by sublimation. Halides formed as sublimation products about volcanic fumarolesinclude sal ammoniac, NH₄Cl; malysite, FeCl₃; and cotunnite, PbCl₂. At Mount Vesuvius, Italy, is the most noted occurrence of such minerals. See also Halide.

5.Meteorites. Lawrencite, FeCl₂, has been found in iron meteorites.