Anhydrite is a calcium sulfate mineral found worldwide, often with halite and other minerals. It can be white, gray, purple, or blue and is relatively soft. Good specimens are sought after by collectors. Anhydrite is part of the evaporite group and can be produced synthetically. It is used in cement production and can transform back into plaster if it absorbs water.
Anhydrite is a sedimentary mineral composed of calcium, sulfur and oxygen. It is also known as calcium sulfate. Good natural anhydrite specimens are often sought after by rock and mineral collectors.
Anhydrite is usually white, colorless or gray. It can also be found in purple or blue tones. When it has a soft blue color it can be referred to as angelite. Scratching the mineral on a striped plate usually results in a white residue. It is relatively soft, only rating 3.5 on the Mohs scale of hardness.
This mineral can be found in many places around the world, including the United States, Mexico, Austria, and Germany. It’s quite common, but good specimens aren’t; it is not a mineral characterized by good crystal formation. Those specimens with good crystal formation are generally the ones sought after by collectors. Crystals generally range from clear to translucent.
This mineral is commonly believed to have been discovered in 1794. It wasn’t until 1804, however, that a German geologist named Abraham Gottlob Werner named it anhydrite. This name refers to the fact that this mineral does not contain water.
This mineral is part of a group known as evaporites. This means that their formation is the result of evaporation. In this case, the anhydrite often results from the dehydration of the gypsum.
If the mineral absorbs water, it can be transformed back into plaster. This alteration is not always complete. In some cases, one part of the specimen may remain anhydrite while the other part becomes gypsum. There have been reports of improperly treated gypsum being sold as anhydrite to unsuspecting buyers.
The true mineral is commonly found underground and in salt basins. In many cases it is found with halite, which is also in the evaporite group. It can also be associated with dolomite, calcite and sylvite.
Anhydrite can also be produced synthetically. One instance where this happens is during the production of hydrofluoric acid. At one time, this synthetic material was considered a problematic waste product. Now it is pulverized and used, for example, to make flooring materials.
It is also used in the production of some types of cement. When used for this purpose, it has several positive characteristics. For example, it can help delay the setting of cement. It can also help ensure that the concrete is of uniform quality.
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