A Geiger counter is used to detect radioactivity.
One of the instruments used is the Geiger counter. It indicates radioactivity by means of a meter, a flashing light, or a clicking sound, which can be heard through earphones. Another instrument for detecting radioactivity is the scintillation counter. It is more sensitive than the Geiger counter and it can detect radioactivity from a greater distance. The scintillation counter can be used from an automobile or an airplane, but the Geiger counter must be quite close to the source of radioactivity to be of use.
Various [uranium minerals] have been found, mostly in small amounts, in a number of places in Texas. Some of these minerals, such as uraninite or [pitchblende], are heavy and dark colored. Others, including [carnotite], tyuyamunite, autunite, and [uranophane], are a shade of yellow or green. They are quite soft. Deposits of the light-colored uranium minerals have been mined from two areas of Texas. One of these areas is in Garza County on the Texas [High Plains], and the other is in Karnes and Live Oak counties in the [Gulf Coastal Plain].
One of the light-colored [uranium minerals], [carnotite], is a potassium-uranium vanadate, which has a bright canary-yellow or lemon-yellow color. This mineral is [transparent] to [translucent] and has an earthy or a pearly luster. Carnotite usually is found as crusts and as powdery masses. It is quite soft and can be scratched with a fingernail.
[Carnotite], along with tyuyamunite, autunite, and several other soft, yellowish or greenish [uranium minerals], is found in the Texas [Gulf Coastal Plain]. These minerals occur in the Jackson, Catahoula, and Oakville strata (which are [Tertiary] in age) in an area extending from Gonzales County to the Rio Grande (in parts of the area indicated by no. 2 and no. 3 on the [geologic map], pp. [4]-5). The largest deposits in this district have been found in the Karnes County area.
The [Gulf Coastal Plain] uranium minerals occur mostly with sandstones and clays in a sequence of strata that contains [volcanic ash]. It is believed that small scattered amounts of uranium compounds that were present in the volcanic ash [sediments] were dissolved by seeping underground water. These waters then moved into the sandstones and clays where they deposited the uranium as [carnotite] and as other [uranium minerals].
Another uranium mineral, [uranophane] (calcium-uranium silicate), also occurs in Texas. Uranophane has a yellow to yellow-orange color and a pearly to greasy luster. When rubbed across a [streak] plate, it leaves a light yellow to a light yellow-orange streak. It is soft enough to be scratched by a copper penny. Uranophane has been found in [extrusive] [igneous rocks] in northwestern Presidio County in west Texas.
A dark-colored uranium mineral, [pitchblende], is a variety of the mineral uraninite, uranium dioxide. Pitchblende does not occur with a crystal shape but rather as rounded and irregular-shaped masses. It is brownish black, greenish black, or black. If you rub it across a [streak] plate, pitchblende leaves a brownish-black streak. This mineral is heavy (it has a [specific gravity] of 6.5 to 8.5) and hard (a pocket knife will not scratch it, although a steel file will). Pitchblende has a submetallic luster and looks dull, greasy, or like pitch or tar.
Small amounts of [pitchblende] have been found at several places in Texas. One of these localities is a few miles west of Burnet in Burnet County in central Texas. Here, the pitchblende occurs in [Precambrian] [igneous rocks] that are associated with [gneiss]. In south Texas, some fine, scattered particles of pitchblende have been found about 325 feet below the surface in [Tertiary] ([Pliocene]) [sediments] that cover the Palangana [salt] dome in Duval County. No pitchblende is mined in Texas.
Uranophane. See [Uranium Minerals].