[Chalcocite], with its dark color, does not look at all like copper, which is a bright reddish brown. Chalcocite, however, is the chief copper mineral at the most important copper mine in Texas, the Hazel mine, which is about 15 miles northwest of Van Horn in Culberson County in west Texas. This mine, although now idle and almost filled with water, has produced about one and a half million pounds of copper along with more valuable silver ores. Here, the chalcocite and other minerals occur in material that fills large cracks in red [sandstone] of the [Precambrian] Hazel [Formation]. It is thought that long ago, molten [igneous] rock material far below the surface sent out hot solutions containing copper and other [elements]. These solutions moved upward and deposited minerals in the [fracture] zone in the sandstone.
[Chalcocite] occurs also in north-central Texas. It is found in Archer, Baylor, [Clay], Foard, Hardeman, King, Knox, Stonewall, and several other counties of this area. Here, it occurs in [Permian] [sedimentary] rocks (called “red beds”) as rounded masses, as scattered grains, and as petrified wood. Because these deposits are far from any [igneous] rocks, they apparently did not form in the same way as those at the Hazel mine. These north-central Texas deposits have never really been commercially developed. During the Civil War, however, some copper from this area was made into percussion caps for the Confederacy.
The Hazel copper-silver mine, Culberson County, Texas, as it appeared in 1951. Photograph by P. T. Flawn.
Another copper mineral, [chalcopyrite], is a copper-iron sulfide. It also is known as copper pyrites and yellow copper ore. This mineral has a metallic luster and a brass-yellow or a golden-yellow color. When rubbed across a [streak] plate, it gives a greenish-black streak. Chalcopyrite will tarnish and then has bronze, blue, purple, and other rainbow-like colors. This mineral is fairly soft—you can scratch it with a pocket knife. Because of chalcopyrite’s yellow color, it has often been mistaken for [gold]. For this reason, it, like iron [pyrite], is often called fool’s gold. (See Gold, [p. 60], for ways to tell them apart.)
[Chalcopyrite] commonly is found in compact masses that show no crystal shapes. These masses either are scattered through rocks or occur in material that fills cracks in rocks.
Some [chalcopyrite] is found in [Precambrian] [sandstone] at the Hazel mine and in other deposits in the Van Horn area of Culberson and Hudspeth counties. It also occurs in Precambrian rocks at the Sheridan and Pavitte prospects in Burnet County. These chalcopyrite localities are in districts where [igneous rocks] occur.
It is likely that, long ago, hot solutions containing copper moved upward, out of deeply buried molten [magma]. While still far below the surface, the solutions deposited the [chalcopyrite] in cracks and other openings in the nearby rocks.
Two [copper minerals] of Texas, [azurite] and [malachite], are copper carbonates. Azurite is commonly called chessylite and blue copper; malachite is called green copper carbonate. Because these minerals are carbonates, a drop of dilute hydrochloric acid will fizz and bubble when placed on either of them.
[Azurite] has a bright, intense blue color and leaves a blue [streak] when rubbed across a streak plate. [Malachite] has a bright green color and leaves a green streak. These minerals have a nonmetallic luster and a glassy to dull appearance. Commonly, they are [translucent], although some specimens of azurite are [transparent]. Both azurite and malachite are fairly soft—a pocket knife will scratch them, but a copper penny will not.