Several other minerals, such as [pyrite], [chalcopyrite], and [mica], are sometimes mistaken for [gold]. None of these, however, is malleable and ductile, and none is nearly as heavy as gold. Pyrite and chalcopyrite have dark-colored streaks unlike that of gold. Mica cleaves so perfectly that it can be split into thin, flat sheets, but gold has no [cleavage] at all.
The best places to look for [gold] are in areas near [igneous rocks] and along the creeks and rivers that drain these areas. It is thought that most gold originally was carried up from molten [igneous] rock by hot solutions. The solutions moved into cracks and other openings in nearby rocks and deposited the gold, commonly along with [quartz]. Later, some of these gold-bearing rocks weathered away. The gold that the rocks contained either remained at the spot or was washed into creeks and rivers. These transported accumulations of loose gold are called placer deposits.
Placer [gold] in very small quantities has been found in some of the stream [gravels] of Texas.
No really important [gold] deposit has ever been found in Texas, although traces and small amounts have been reported in several areas. A little gold has been found in the [Llano uplift] area of central Texas. It occurs in [quartz] veinlets that cut through some of the [Precambrian] [metamorphic rocks] of Llano, Mason, northeastern Gillespie, and west-central Burnet counties. Many years ago, a small amount of gold was mined northeast of Llano in Llano County from the Heath mine. Some gold also has been found in sands and [gravels] along streams, such as along Sandy Creek and its tributaries, in parts of this Llano uplift area.
In the Trans-Pecos country of west Texas, small amounts of [gold] have been found in the Van Horn area of Culberson and Hudspeth counties, in the Quitman Mountains district of Hudspeth County, and in the country around Shafter in Presidio County. Most of the small quantity of gold that was mined in west Texas was obtained as a by-product from the Presidio mine in the Shafter district (described with [silver minerals] on [p. 90]).
Small amounts of [gold] have been reported from other parts of Texas. Some of these localities are in [Eocene] [Tertiary] sandstones in the [Gulf Coastal Plain], in [Cretaceous] limestones in Irion, Uvalde, and Williamson counties, and in [sand] and [gravel] in Howard and Taylor counties. None of these deposits has been found to have any commercial value.
Granite
[Granite] is an [intrusive] [igneous] rock that is made up chiefly of [crystalline] grains or crystals of [quartz] and a [feldspar] mineral, such as [orthoclase] or [microcline]. Several other minerals, including [mica] and hornblende, may also be present.
All of the mineral grains in [granite] are about the same size, and you can distinguish them without using a magnifying glass. A granite may be coarse grained, medium grained, or fine grained. When you examine this rock, you will see that its grains are not cemented but interlocked like the pieces of a jigsaw puzzle. The color of granite, which is pink, red, gray, or brownish, depends chiefly on the color of its [feldspar] grains.