Albite. See [Feldspar].
Almandite. See [Garnet].
Amethyst. See [Quartz].
Amphibole Asbestos. See [Asbestos].
Anhydrite
[Anhydrite], calcium sulfate, is a rather soft mineral that you can scratch with a pocket knife, although not with a fingernail. It has a glassy or a pearly luster and is [transparent] or [translucent]. Most anhydrite is white, but impurities cause it to be grayish, bluish, or reddish. When rubbed across a [streak] plate, anhydrite gives a white streak. This mineral has an uneven [fracture], and it cleaves in three directions that are at right angles to each other. It commonly occurs as rectangular [cleavage fragments] or as sugary [crystalline] masses.
[Anhydrite] resembles [dolomite], [limestone], or [gypsum]. You can use a hardness test to distinguish it from gypsum (anhydrite is harder) and an acid test to distinguish it from limestone and dolomite. A drop of dilute hydrochloric acid will fizz when you put it on limestone or powdered dolomite. On anhydrite, the acid does not fizz.
[Anhydrite] occurs at several places in Texas. It is, for example, seen in bluffs along the Double Mountain Fork and the [Salt] Fork of the Brazos River in north-central Texas. Most of the Texas anhydrite, however, occurs underground. In the [Gulf Coastal Plain], the anhydrite is found below the surface in salt domes. (Salt domes are described with [halite] on [p. 66] and with [sulfur] on [p. 91].)