Themes > Science > Earth Sciences > Oceanography > Ocean Sediments > Evaporites > Evaporites-Halite and Anhydrite

halite

The Mineral Anhydrite or Angelite

  • Chemistry: CaSO4, Calcium Sulfate
  • Class: Sulfates
  • Uses: in the manufacture of some cement, a source of sulfate for sulfuric acid.
  • Specimens
Anhydrite is a relatively common sedimentary mineral that forms massive rock layers. Anhydrite does not form directly, but is the result of the dewatering of the rock forming mineral Gypsum (CaSO4-2H2O). This loss of water produces a reduction in volume of the rock layer and can cause the formation of caverns as the rock shrinks. Good mineral specimens of Anhydrite were extremely rare dispite its common occurrance. However, fine specimens of Anhydrite have been found in Mexico and Peru that show good crystal habit, a nice blue color and even a play of light internally in the crystal.

Lilac blue Anhydrate is sometimes called Angelite, for it's "Angelic" color.

Physical Characteristics:

  • Color is ordinarily white, gray or colorless but also blue to violet.
  • Luster is vitreous.
  • Transparency crystals are transparent to translucent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include the tabular, rectangular box formed by three pinacoids, often elongated in one direction forming a prismatic crystal. Most commonly massive and granular.
  • Cleavage is in three directions forming rectangles, but perfect in one, very good in another and only marginally good in the third direction.
  • Fracture is conchoidal.
  • Hardness is 3.5
  • Specific Gravity is approximately 3.0 (average for translucent minerals)
  • Streak is white.
  • Associated Minerals are calcite, halite, and ocassionally sulfides such as galena and pyrite.
  • Other Characteristics: some specimens fluoresce under UV light.
  • Notable Occurances include Mexico; Peru; Germany and New Mexico.
  • Best Field Indicators are crystal habit, rectangular and non-uniform cleavage and low density.


Information provided by: http://hjs.geol.uib.no