Sulfur
[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.