Name/Title
AnhydriteEntry/Object ID
2014.1.139Description
Chemical Composition: CaSO4
Crystal System: Orthorhombic System
Description: Common Name: Anhydrite
Chemistry: CaSO4, Calcium Sulfate
Group: Sulfides
Location: Chihuahua, Mexico
Description:A very pale blue crystal of anhydrite with a couple of patches of small calcite crystals, colored a light sky blue with sploches of white, silver, and grey.
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.
Best Field Indicators are crystal habit, rectangular and non-uniform cleavage and low density.
Fracture: conchoidal
Hardness: 3 Calcite
Luster: Vitreous
Occurrence: 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.
Anhydrite is most frequently found in evaporite deposits with gypsum; In this occurrence depth is critical since nearer the surface anhydrite has been altered to gypsum by absorption of circulating ground water.
Rock Type: Sedimentary
Specific Gravity: 3.0
Streak: white
Texture: crystaline
Variety: 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 vitreous. When exposed to water, anhydrite readily transforms to the more commonly occurring gypsum, (CaSO4·2H2O) by the absorption of water. Anhydrite is commonly associated with calcite, halite, and sulfides such as galena, chalcopyrite, molybdenite and pyrite in vein deposits.
The specimen we have on display lilac blue Anhydrate is sometimes called Angelite, for it's "Angelic" color. Anhydrite also come in a variety of colors.Collection
RAGM Mineral CollectionAcquisition
Accession
2014.1Source or Donor
Crater Rock Museum (unknown donors)Acquisition Method
GiftDimensions
Width
4 inDepth
2-1/4 inLength
4 inDimension Notes
Dimension taken at widest pointsLocation
Location
Display Case
FS-4-ARoom
Frieda Smith HallBuilding
Crater Rock MuseumCategory
ExhibitMoved By
Ian C.Date
January 29, 2025Notes
Major mineral groups installationLocation
Display Case
FS-9Room
Frieda Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
Ian CunninghamDate
December 27, 2023