Sulfur is one of Texas’ most valuable minerals. It consists of only a
single element, sulfur. This mineral has a resinous luster and is
transparent to translucent. Sulfur ordinarily is yellow, but impurities
cause it to look greenish, brownish, reddish, or grayish. When you rub
it across a streak plate, it leaves a white or a pale-yellow streak.
Sulfur has a specific gravity of 2.04 to 2.09 and is soft enough to be
scratched by a copper penny. It breaks with a conchoidal to uneven
fracture. When it gets hot enough (478° Fahrenheit), sulfur will burn.
For this reason, it often is called _brimstone_.
Sulfur does not conduct electricity and is a poor conductor of heat. You
can test how poorly heat passes through it by holding a fragment of
sulfur up to your ear. You may be able to hear a crackling sound. The
sound results when the outer part of the fragment expands (due to the
heat from your hand) while the inner part (which has received no heat)
remains unchanged.
Crystals of sulfur are sometimes found, and most of them have either a
double-pyramid shape or a flat, tabular shape. Sulfur also occurs as
compact masses, as crusts, and as scattered grains.
Native sulfur deposits are found in two widely separated areas of
Texas—one in west Texas and the other along the Gulf Coast in southeast
Texas, extending over into Louisiana. In the Gulf Coast area, native
sulfur is found on some of the salt domes.
The salt domes are huge (from about half a mile to more than 2 miles
across), column-shaped masses made up of halite and some anhydrite.
These masses have pushed up toward the surface through thousands of feet
of sand, clay, and other sedimentary rocks. On top of many of the salt
columns is a covering of limestone (calcite), anhydrite, and gypsum
known as the _cap-rock_. It is in this cap-rock that the sulfur is
found.
It is thought that when the masses of halite and anhydrite pushed toward
the earth’s surface, some of the upper part of the halite dissolved. The
anhydrite, however, did not dissolve, and it remained on top of the salt
column. Then, a part of this anhydrite was altered into the gypsum,
limestone, and sulfur that now are found in some of the cap-rocks.
Laboratory experiments have shown that the sulfur in the cap-rocks
likely formed through the action of sulfate-reducing bacteria. These
bacteria, in the presence of petroleum, converted the sulfate in some of
the anhydrite into hydrogen sulfide. Later, hydrogen sulfide was
oxidized—perhaps by reaction with more of the anhydrite—to form the
sulfur.
Most of the large cap-rock sulfur deposits are about 1,500 to 2,400 feet
underground. At first, an attempt was made to get this sulfur out of the
ground by digging shafts down to it, but loose, wet, caving sands and
poisonous gases, such as hydrogen sulfide, made this mining method
almost impossible. Finally, a chemist, Herman Frasch, found a way to
obtain the sulfur by making use of sulfur’s low melting point. When
sulfur gets slightly hotter than boiling water (235° to 247°
Fahrenheit), it melts and becomes a dark, yellowish-brown liquid.
In the Frasch method of sulfur mining, a well is drilled into the
salt-dome cap-rock, and three pipes, one inside the other, are put into
the well. Superheated water under pressure (hotter than 212° Fahrenheit,
the temperature at which water ordinarily turns into steam) is sent down
one of the pipes to melt the sulfur in the cap-rock around the bottom of
the well. Then, compressed air is sent down another of the pipes. This
air presses against the liquid sulfur and forces it up to the surface
through the third pipe. At the surface, the sulfur is poured into bins,
where it cools and becomes a solid again, or it is transported molten,
in pipelines and tankers.
Sulfur has been obtained from a number of the Texas Gulf Coast salt
domes including Bryan Mound, Clemens dome, Damon Mound, and Hoskins
Mound in Brazoria County; Palangana dome in Duval County; Long Point
dome, Nash dome, and Orchard dome in Fort Bend County; High Island dome
in Galveston County; Fannett dome and Spindletop dome in Jefferson
County; Moss Bluff dome in Liberty County; Gulf dome in Matagorda
County; and Boling dome in Wharton County.
In west Texas, sulfur occurs in Permian rocks both at the surface and
underground. A small amount of sulfur has been mined in the Rustler
Springs area of northeastern Culberson County and northwestern Reeves
County, about 50 miles northwest of Pecos. There, scattered grains,
crystals, and irregular masses of sulfur occur in cracks and in
dissolved-out openings in the Castile Gypsum and in the surface gravel,
gypsum, sand, and clay that cover most of this formation.
Sulfur has many uses. It is used as an insect-killer, thus helping our
food crops to grow. It is used in pulp and paper manufacturing and in
the vulcanizing of rubber. Some other uses are in the making of paints,
dyes, and explosives. A large amount of sulfur goes to make sulfuric
acid, which itself has numerous uses in the chemical, steel, oil
refining, and other industries.
[Illustration: Sulfur is obtained from the cap-rock of Gulf Coastal
Plain salt domes by the Frasch process.]
Sulfur
Uncemented Sediments
Limestone
Sulfur-Bearing Limestone
Hot Water
Melted Sulfur
Anhydrite