Galena, lead sulfide, is a shiny, lead-gray, metallic mineral that has a
specific gravity of 7.4 to 7.6. It is soft enough to mark paper, and it
leaves a grayish-black streak on a streak plate. This mineral cleaves
perfectly in three directions, and the cleavage fragments have square
corners—some are cubes.
Galena occurs as cleavable masses, as fine or coarse grains, and as
crystals, most of which are cubes. Galena commonly is associated with
other minerals; for example, some of the west Texas galena either
contains some silver (then called _argentiferous galena_) or occurs with
it. Sphalerite, a zinc mineral, is commonly found with galena.
Galena is an important mineral because it is the chief source of lead.
Compounds of lead, called white lead, red lead, and litharge, are used
as paint pigments. Automobile batteries contain lead plates, and
tetraethyl lead is added to gasoline to keep the car’s motor from
knocking. Some other uses of lead are in bullets, type metal, solder,
and cable coverings.
[Illustration: Galena has perfect cubic cleavage. The three directions
of cleavage are at right angles to each other resulting in cubic
cleavage fragments.]
Galena has been found in several areas of Texas and has been mined in
central and west Texas. None, however, has been produced in recent
years. Most of the galena mined in west Texas was obtained from silver
mines, where the galena was a by-product. Some of the west Texas galena
deposits are at Altuda Mountain east of Alpine in Brewster County, in
the Eagle Mountains and the Quitman Mountains in Hudspeth County, and in
the Chinati Mountains and the Shafter area in Presidio County. Most of
the mining has been from the Shafter area (this area is described with
silver minerals on p. 90).
In central Texas, several small galena deposits have been found in
Blanco, Burnet, and other counties of the Llano uplift area. Some galena
has been mined at Silver Creek in northwestern Burnet County. Here,
galena occurs in cracks and as scattered grains in Cambrian limestones
and sandstones.
It is probable that much of the galena in west Texas and in central
Texas was formed when hot magma forced out solutions containing lead.
These solutions moved up through cracks and other openings in the
subsurface rocks and deposited the galena in them.
Small amounts of galena, which likely had a different origin, have been
found in Fisher, Foard, Hardeman, and Young counties. A little occurs
also in rocks associated with salt in a number of the Gulf Coastal Plain
salt domes.