Selenite variety of Gypsum

Selenite...is a variety of Gypsum... and is one of the most common, rock-forming minerals, developing thick beds formed by the evaporation of extremely salt laden waters. Gypsum is associated with halite and sulfur. It is deposited from lakes, seawater, hot springs, volcanic moisture, and sulfate solutions in underground veins. Anhydrite in underground veins can be converted into gypsum by hydration from groundwater close to surface areas. Gypsum dissolves over time in water, and is rarely found in the form of sand.

A well known oddity is the White Sands National Monument in the state of New Mexico. The unique conditions there have produced a 275 square mile area of white gypsum sand. In 1933 President Herbert Hoover declared the gypsum dunes a protected national monument to prevent commercialization of the area.

When heated under appropriate conditions, gypsum forms plaster of Paris. Gypsum is extremely useful for many practical applications and for works of art. In particular, it is used for wallboard for buildings, as a component of concrete for the construction of highways and bridges, and as a soil conditioner for agriculture. The Clear variety is called selenite. The translucent variety, called alabaster, is a valuable ornamental stone. When converted to plaster of Paris, it is used in sculpture, architecture, fire protection, and theatrical sets. There are many formations of Gypsum that make outstanding collection specimens, and it is a favorite of rockhounds!

For a description from Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Gypsum