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.