Sulfates and Chromates

Sulfates and Chromates

The most common of the sulfate minerals, this mineral is found in marine evaporites, in caves, fumaroles, and in the oxidized zones of sulfide deposits. When formed as clear crystals, it is referred to as selenite. The fibrous variety is known as satin spar and also forms in "roses." It is used chiefly for the production of plaster of Paris, wallboard, and fertilizer. It is named in antiquity from the Greek, meaning “plaster.”

This mineral has a bright hyacinth-red color and an orange-yellow streak. It is commonly found as crystals, which are translucent with an adamantine luster. It is not abundant enough to be of commercial value, but it is of historic interest because the element chromium was first discovered in crocoite. Its name is from the Greek word meaning "saffron," in allusion to the color.

Chalcanthite is a rare mineral due to being a water-soluble sulphate. It is a secondary blue-colored mineral formed in arid climates or in rapidly oxidizing copper deposits. It usually forms post-mining, crystallizing on mine walls and by the action of acidic surface waters on copper veins. It was discovered in 1853 at the Chuquicamata Mine, Chile, where it is an important ore mineral. It is named from two Greek words meaning "brass/copper" and "flower."

By far the most common strontium mineral, celestite closely resembles barite. It is used in the preparation of strontium nitrate for fireworks and tracer bullets and other strontium salts used in the refining of beet sugar. It was named in 1791 from the Greek word for "celestial", in allusion to the faint blue color of the original specimen.

Also spelled “barite,” this mineral is recognized by its high specific gravity and characteristic cleavage and crystals. It is a common mineral of wide distribution, occurring as a gangue mineral in hydrothermal veins and limestone. More than 80% of this mineral is used in the oil and gas industry as a drilling mud. It is named from the Greek word meaning "heavy," in allusion to its high specific gravity.

Named after the type locality at the Antler Mine in Arizona, this mineral is a secondary mineral occurring in the oxidized zone of copper deposits in arid regions. It was the chief ore mineral at Chuquicamata, Chile, the largest open pit copper mine in the world.

A minor ore of lead, this mineral was discovered in 1832 on the island of Anglesey, from which it is named, in Wales, United Kingdom. It is recognized by its high specific gravity, adamantine luster, and association with galena. It is a common supergene mineral found in the oxidized portions of lead deposits.

Named after the Latin word for “alum”, this mineral is also called “alumstone.” It was discovered in Latium, Italy, in 1824 and is formed by sulfuric acid solutions acting on rocks rich in potash feldspar. In Marysvale, Utah, it has been mined and treated to recover potassium and aluminum.

The basic unit of the sulfate minerals are the SO4 groups. These groups combine with metals to form the sulfate minerals. Barite, gypsum, and anhydrite are the most common sulfate minerals.

Minerals of the sulfate class:

  • Have vitreous luster.
  • Have average to above average density.
  • Have average hardness.
  • Originally formed in veins, oxidation zones, contact metamorphic zones and evaporite deposits.
  • Are, in some cases, soluble.
  • Are, in several cases, fluorescent.