Gypsum

Size is the decisive factors affecting the price of gypsum. The price of a 2.5 - 8 cm stone is usually $2-$10/piece.

Gypsum is difficult to facet due to its fragility and softness. Among choice samples, transparency and clarity are notable factors affecting value. A large number of synthetics have been developed, but these have industrial applications and are not known to be used in the jewelry trade. It is more common for gypsum to be used to fake other materials such as moonstone.

Gypsum has been used for many different applications throughout history. One white variant is called alabaster and was a popular material for sculpture since antiquity. Today, gypsum is a key ingredient in many fertilizers, plasters and cements, as well as used in some food preparation.

Gypsum is represented by a famous work of art by Vincent Van Gogh entitled the gypsum Torso. Painted in Paris in the late 1880s, it is a still life representing a headless and armless female body, like an ancient greek statue.

Gypsum is a common mineral, with thick and extensive evaporite beds in association with sedimentary rocks. Deposits are known to occur in strata from as far back as the Archaean eon. Gypsum is deposited from lake and sea water, as well as in hot springs, from volcanic vapors, and sulfate solutions in veins. Hydrothermal anhydrite in veins is commonly hydrated to gypsum by groundwater in near-surface exposures. It is often associated with the minerals halite and sulfur. Gypsum is the most common sulfate mineral. Pure gypsum is white, but other substances found as impurities may give a wide range of colors to local deposits. Because gypsum dissolves over time in water, gypsum is rarely found in the form of sand. However, the unique conditions of the White Sands National Park in the US state of New Mexico have created a 710 km (270 sq mi) expanse of white gypsum sand, enough to supply the US construction industry with drywall for 1,000 years. Commercial exploitation of the area, strongly opposed by area residents, was permanently prevented in 1933 when President Herbert Hoover declared the gypsum dunes a protected national monument. Gypsum is also formed as a by-product of sulfide oxidation, amongst others by pyrite oxidation, when the sulfuric acid generated reacts with calcium carbonate. Its presence indicates oxidizing conditions. Under reducing conditions, the sulfates it contains can be reduced back to sulfide by sulfate-reducing bacteria. This can lead to accumulation of elemental sulfur in oil-bearing formations, such as salt domes, where it can be mined using the Frasch process Electric power stations burning coal with flue gas desulfurization produce large quantities of gypsum as a byproduct from the scrubbers. Orbital pictures from the Mars Reconnaissance Orbiter (MRO) have indicated the existence of gypsum dunes in the northern polar region of Mars, which were later confirmed at ground level by the Mars Exploration Rover (MER) Opportunity.

Gypsum is found as different varieties in nature. The transparent and cleavable variety is called selenite. The silky and fibrous variety is commonly called satin spar. The granular and massive variety is named as alabaster. In arid areas, gypsum can occur in a flower-like form, typically opaque, with embedded sand grains called desert rose.