HALITE
Halite is true salt, which consists of sodium chloride
(NaCl). This is the same chemical long used as flavoring on food & as
a preservative. It has a nonmetallic luster, typically clearish/coloress,
and is relatively soft (H = 2.5). Halite forms cubic crystals and has
cubic cleavage (= 3 cleavage planes meeting at 90º angles). Halite is
most readily identified by its strongly salty taste.
Halite has economic value. In addition to its
use in food, salt is traditionally used in large quantities in wintertime to
prevent roadways from icing up. Halite is principally mined from ancient
rock salt successions. Rock salt is a chemical sedimentary rock composed
of halite and formed by evaporation of seawater. Northeastern Ohio has
significant & economic subsurface concentrations of rock salt (halite) of
Silurian age.
Halite
(~1 to ~2 cm across each)
Halite
(each ~2 to ~4 mm in size) - small masses of modern lacustrine evaporitic halite
crystals from Grosbeak Lake Salt Flats, SSW of town of Fort Smith, far-northern
Alberta Province, western Canada.
Hopper halite from Trona, California, USA. The
edges of halite crystals can grow more quickly than the faces, resulting in a
series of depressed faces. Such crystals are called "hopper
crystals".
(Dwyer Mercer County District Library #223-550,
Celina, Ohio, USA).
Blue halite, a rare color variety (left: 2.6 cm across; right: 2.9
cm across). The blue coloration is the result of radiation from
potassium-40 in nearby potash salts. Irradiation ultimately results in
excess free sodium metal in the halite, turning it blue. These come from
the Prairie Evaporite Formation (upper Elk Point Group, Middle Devonian) of the
Potash Saskatchewan-Lanigan Mine (PCS-Lanigan Mine, near Lanigan, south-central
Saskatchewan, Canada).