Halite, sodium chloride, is the table salt you sprinkle on food for
seasoning. This mineral ordinarily is white or colorless, but other
materials cause it to be tinted red, blue, gray, brown, or green. When
you rub halite across a streak plate, it leaves a white streak.
Because halite cleaves in three directions, all at right angles to each
other, the cleavage fragments are shaped like cubes. You can see some of
them by looking at a few grains of table salt through a magnifying
glass.
Halite has a salty taste and dissolves easily in water. It also is
transparent to translucent and has a glassy luster. This mineral is soft
enough for a copper penny to scratch it. Halite commonly occurs as cubic
crystals and as granular or compact masses.
In addition to its use as table salt, much halite goes to make soda ash,
chlorine, and other chemicals. A few of its other uses are in leather
making, meat packing, and food canning.
Texas has large underground deposits of halite. These deposits, known as
_rock salt_, occur in the Permian subsurface basin of west Texas and in
the salt domes of the Gulf Coastal Plain. The Permian basin, which
extends under parts of west Texas, New Mexico, Oklahoma, Colorado, and
Kansas, is now completely filled with sediments. It appears level and
flat when you travel across it and does not look at all like a basin or
a valley. During Permian time, however, this area was covered by a salty
sea. As the sea gradually dried up, the dissolved material that it
contained was deposited as thick beds of halite, anhydrite, and other
minerals. Later, these minerals were covered by sedimentary rocks which
were deposited on top of them. Now, the minerals are found many hundreds
of feet below the surface. In Hutchinson, Mitchell, Ward, and Yoakum
counties, some of this Permian basin salt has been produced (as brine)
from wells that have been drilled into it.
[Illustration: Salt domes, which are huge, underground columns of
halite, occur on the Gulf Coastal Plain.]
The Gulf Coastal Plain salt domes are huge and almost circular columns
of halite, some of which are more than 2 miles wide. Some are less than
300 feet below the surface, but most of them are much deeper. These salt
columns pushed upward many thousands of feet from great, deeply buried
salt deposits. The halite is mined from shafts dug into the Hockley salt
dome in Harris County and into the Grand Saline salt dome in Van Zandt
County. Salt brines are produced from wells drilled into several salt
domes of this area.
At the surface in Texas, halite occurs in salt lakes in Crane and
Hudspeth counties and in alkali lakes on the High Plains. It is found
also on the shores of bays and lagoons in Cameron, Kenedy, Kleberg, and
Willacy counties, and it occurs at springs and seepages in various
places in the State.