WorldWide Drilling Resource

This month we are focusing on two minerals, anhydrite and antimony. One is a native mineral which occurs in a natural state, and one is an evaporite mineral which is formed by the evaporation of water. Anhydrite is an evaporite mineral occurring in extensive layered deposits in sedimentary basins where large volumes of seawater have evaporated. It is typically interbedded with halite, gypsum, and limestone in accumulations up to hundreds of feet thick. Closely related to gypsum, anhydrite’s name comes from the Greek word anhydrous which means “without water”. It converts to gypsum under humid conditions, or when it is in contact with groundwater. This transition involves the absorption of water and a significant change in volume. Conversely, if gypsum is heated to about 390ºF (200ºC), the water will evaporate and it will convert to anhydrite. Anhydrite is used as a drying agent in plaster, paint, and varnish. It is also used along with gypsum to produce plaster, joint compound, wallboard, and other products for the construction industry. Anhydrite has also been used as a source of sulfur in the production of sulfuric acid. Hydrofluoric acid is produced using fluorite and sulfuric acid and for every ton produced, about 3½ tons of synthetic anhydrite is produced. For decades, synthetic anhydrite was considered a nuisance product for disposal, but now it can be dried in a kiln and used for producing cement, plaster, and flooring, as well as used as a filler in the production of plastics and paper products. Antimony was named after the Greek words anti and monos which means “a metal not found alone.” Antimony is not abundant, but it is found in over 100 mineral species. Although it is considered a native element which can occur in a natural state, it is rarely pure and almost always contains arsenic, and may also contain traces of silver, iron, and sulfur. Antimony and arsenic are almost identical. In some cases, complex scientific tests are the only way to tell them apart. The natural sulfide of antimony was used in Biblical times as medicine and as a cosmetic. Today, the pure form of antimony is used to make certain types of semiconductor devices, such as diodes and infrared detectors. An alloy of lead and antimony is used in batteries, low-friction metals, small arms, and tracer bullets, cable sheathing as well as other products. Other compounds of antimony are used to make flame- proofing compounds, paints, ceramic enamels, glass, and pottery. It is also used for medicinal research and as a dye to color glass. The majority of antimony is consumed in the production of antimony trioxide, the compound used in flame-retardant materials such as children’s clothing and toys, as well as aircraft and auto seat covers. When combined with halogenated particles, it suppresses, reduces, or delays the spread of flame. It is incorporated into adhesives, paints, plastics, rubber insulation, decorative foams, building materials, and textiles, including upholstered furniture. The World of Minerals 23 WorldWide Drilling Resource ® JUNE 2017