Calcium sulfate in the context of "Anhydrous"

Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO₄·2H₂O. It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk chalk. Gypsum also crystallizes as translucent crystals of selenite. It forms as an evaporite mineral and as a hydration product of anhydrite. The Mohs scale of mineral hardness defines gypsum as hardness value 2 based on scratch hardness comparison.

Fine-grained white or lightly tinted forms of gypsum known as alabaster have been used for sculpture by many cultures including Ancient Egypt, Mesopotamia, Ancient Rome, the Byzantine Empire, and the Nottingham alabasters of Medieval England.

The Winogradsky column is a simple device for culturing a large diversity of microorganisms. Invented in the 1880s by Sergei Winogradsky, the device is a column of pond mud and water mixed with a carbon source such as newspaper (containing cellulose), blackened marshmallows or egg-shells (containing calcium carbonate), and a sulfur source such as gypsum (calcium sulfate) or egg yolk. Incubating the column in sunlight for months results in an aerobic/anaerobic gradient as well as a sulfide gradient. These two gradients promote the growth of different microorganisms such as Clostridium, Desulfovibrio, Chlorobium, Chromatium, Rhodomicrobium, and Beggiatoa, as well as many other species of bacteria, cyanobacteria, and algae.

The column provides numerous gradients, depending on additive nutrients, from which the variety of aforementioned organisms can grow. The aerobic water phase and anaerobic mud or soil phase are one such distinction. Because of oxygen's low solubility in water, the water quickly becomes anoxic towards the interface of the mud and water. Anaerobic phototrophs are still present to a large extent in the mud phase, and there is still capacity for biofilm creation and colony expansion. Algae and other aerobic phototrophs are present along the surface and water of the upper half of the columns.

Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO₄. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium (baryte) and strontium (celestine) sulfates, as might be expected from the chemical formulas. Distinctly developed crystals are somewhat rare, the mineral usually presenting the form of cleavage masses. The Mohs hardness is 3.5, and the specific gravity is 2.9. The color is white, sometimes greyish, bluish, or purple. On the best developed of the three cleavages, the lustre is pearly; on other surfaces it is glassy. When exposed to water, anhydrite readily transforms to the more commonly occurring gypsum, (CaSO₄·2H₂O) by the absorption of water. This transformation is reversible, with gypsum or calcium sulfate hemihydrate forming anhydrite by heating to around 200 °C (400 °F) under normal atmospheric conditions. Anhydrite is commonly associated with calcite, halite, and sulfides such as galena, chalcopyrite, molybdenite, and pyrite in vein deposits.

Tofu (Japanese: 豆腐, Hepburn: Tōfu; Korean: 두부; RR: dubu, Chinese: 豆腐; pinyin: dòufu) or bean curd is a food prepared by coagulating soy milk and then pressing the resulting curds into solid white blocks of varying softness: silken, soft, firm, and extra (or super) firm. It originated in China and has been consumed for over 2,000 years. Tofu is a traditional component of many East Asian and Southeast Asian cuisines; in modern Western cooking, it is often used as a meat substitute.

Nutritionally, tofu is low in calories, while containing a relatively large amount of protein. It is a high and reliable source of iron, and can have a high calcium or magnesium content depending on the coagulants (e.g. calcium chloride, calcium sulfate, magnesium sulfate) used in manufacturing. Cultivation of tofu, as a protein-rich food source, has one of the lowest needs for land use (1.3 m/ 1000 kcal) and emits some of the lowest amount of greenhouse gas emissions (1.6 kg CO₂/ 100 g protein).

Bassanite is a sulfate mineral composed of calcium sulfate hemihydrate, with the chemical formula CaSO₄·0.5H₂O or 2CaSO₄·H₂O. It has half a water molecule per CaSO₄ unit.

Bassanite was first described in 1910 for an occurrence on Mount Vesuvius. It was named for Italian paleontologist Francesco Bassani (1853–1916).

Drywall (also called plasterboard, dry lining, wallboard, sheet rock, gib board, gypsum board, buster board, turtles board, slap board, custard board, gypsum panel and gyprock) is a panel made of calcium sulfate dihydrate (gypsum), with or without additives, typically extruded between thick sheets of facer and backer paper, used in the construction of interior walls and ceilings. The plaster is mixed with fiber (typically paper, glass wool, or a combination of these materials); plasticizer, foaming agent; and additives that can reduce mildew, flammability, and water absorption.

In the mid-20th century, drywall construction became prevalent in North America as a time- and labor-saving alternative to lath and plaster.

Sidewalk chalk is typically large and thick sticks of chalk made of calcium sulfate (gypsum), instead of calcium carbonate (rock chalk). It comes in multiple colors and is mostly used for drawing on pavement or concrete sidewalks, frequently four square courts or hopscotch boards. Blackboard chalk, typically used in educational settings, is shorter and thinner than sidewalk chalk.

There are several different types of sidewalk chalk, typically coming in solid-colored sticks. 3-D sidewalk chalk sets, in which each stick of chalk is created with two particular colors that appear 3-dimensional when viewed through the 3-D glasses that come with the chalk, also exist.

The Naica Mine of the Mexican state of Chihuahua, is a lead, zinc and silver mine. Located in Naica in the municipality of Saucillo, the Naica Mine is owned by Industrias Peñoles, the world's largest silver producer. Caverns discovered during mining operations contain gigantic crystals of CaSO
₄ · 2 H
₂O (calcium sulfate dihydrate, gypsum, also sometimes called selenite). Peñoles announced in October 2015 that it was indefinitely suspending operations due to uncontrollable flooding at the Naica Mine.

The peak underground air temperature was 58°C (136°F) with 100% relative humidity, which rapidly exposed the visitors to hyperthermia hazard and caused breathing difficulties. Because of the heat, unprotected researchers could only stay up to 10 minutes inside the cave. Longer visits required the use of a special suit fitted with a cooling system (ice reserve in a backpack with cooled water recirculating in polymer tubes installed over all the body surface) and delivering fresh air for easier breathing. The visits were limited to about half an hour, the time needed to melt the ice reserves.