[Bentonite] is used as a drilling-fluid additive in the rotary method of drilling for petroleum and gas.
Some [bentonite] is used to absorb unwanted coloring material in petroleum and in vegetable oils. It is then known as a bleaching [clay]. Bentonite bleaching clay is obtained from some of the [Tertiary] [formations] along the Texas [Gulf Coastal Plain]. It has been produced in Angelina, Fayette, Gonzales, [Jasper], Walker, and other counties in this area.
Another important use of [bentonite], and of other [clay], too, is as drilling mud. In the rotary method of drilling for oil and gas, mud is pumped down into the drilled hole. This mud carries the rock cuttings up to the surface, it cools the drilling tools, and it coats and seals the walls of the hole. Along the [Gulf Coastal Plain], drilling clay is obtained from [Tertiary] [formations].
Common Opal. See [Opal].
Copper Minerals ([Chalcocite], [Chalcopyrite], [Malachite], [Azurite])
A number of minerals containing copper, such as [chalcocite], [chalcopyrite], [malachite], and [azurite], occur in small deposits in Texas. They are found chiefly in the [Llano uplift] area of central Texas, in the Van Horn area of Culberson and Hudspeth counties in west Texas, and in a group of counties in north-central Texas.
Copper is an important [element]. Because it is an unusually good conductor of electricity (only silver, which costs much more, is a better one), it is used for many kinds of wires for switchboards, generators, motors, telephone and telegraph equipment, and light and power lines.
Manufacturers commonly combine copper with other [elements]. For example, some copper is mixed with zinc to make brass and with tin and a little zinc to make bronze. These mixtures are called alloys. Many products are made from copper alloys, including tubing, pipes, jewelry, pots, and pans. Even our coins contain copper.
Sometimes, a prospector uses a chemical test to find out if copper is present in a mineral. First, he crushes a small sample of what he believes is a copper mineral (such as [chalcocite], [chalcopyrite], [azurite], or [malachite]). He then puts the sample in a glass jar or test tube and pours in a small amount of dilute nitric acid (this acid, like hydrochloric acid, is poisonous). After the sample has dissolved in the acid, he adds enough ammonium hydroxide to make the solution alkaline. If the sample is a copper mineral, the solution turns a deep-blue color.
One of the [copper minerals], [chalcocite], copper sulfide, also is known as copper glance. It is a metallic mineral that commonly tarnishes to a dull black. By chipping off a fragment to obtain a fresh surface, you will see that it has a shiny lead-gray color. Chalcocite is rather soft, and it is [sectile], that is, a knife will cut through it as well as scratch it. When you rub chalcocite across a [streak] plate, it gives a grayish-black streak. This mineral commonly occurs as compact masses or as [granular] masses.