Gypsum

Gypsum

Introduction:

Gypsum is one of the most common minerals in sedimentary environments. The word gypsum is derived from the Greek word chalk or plaster and chemically known as Hydrated Calcium Sulphate and its chemical formula for gypsum is Ca(SO4).2H2O. It contains 32.57% CaO, 46.50% SO3 and 20.93% H2O. It is a major rock forming mineral that produces massive beds. It is formed due to the interaction of limestone with sulphurous water. It can easily form from saline water. Gypsum has many inclusions of other minerals. Gypsum is having other name gypsite. Gypsum has the same composition as anhydrate but it contains water in its structure, whereas anhydrate means ‘no water’. The associated minerals of gypsum are calcite, sulphur, halite, borax.

Varieties of gypsum:

There are 3 varieties of gypsum namely selenite, alabaster and satin spar. Gypsum occurs in nature as flattened and as twinned crystals, transparent cleavable masses called selenite. Gypsum also occurs in the fibrous form, called as satin spar. Gypsum is quite compact and vey fined grained variety, called as alabaster. In arid areas gypsum can occur in a flower like form with embedded sand grain called desert rose.


Physical properties of gypsum:

· It is colourless to white, with impurities looks as yellow. Sometimes it is tan, blue, pink, reddish brown or grey.
· Crystal habit is massive, flat, elongated and it is in prismatic.
· Hardness is 1.5 – 2.
· Streak is white.
· Luster is vitreous to silky.
· Fracture is uneven.
· Crystal system is monoclinic 2/m.
· Transparency is opaque.
· It can be soluble in hard dilute HCl.


Industrial applications:

· Gypsum used in cement industry to control the setting time of cement.
· Plaster of Paris can be made by heating gypsum to above 3000 F and removing 75% of water.
· In plaster of paris form it is utilized in construction industry for making wall boards, decorative roofing.
· It is used as a flux for creating earthenware and can be used as a fertilizer.
· Selenite is used for making gypsum plate for petro logical microscope.
· Alabaster and satin spar varieties are used for decorative models.
· Low grade gypsum is used in all countries for agricultural purpose.


World resources of gypsum:

Gypsum is a very common mineral, and occurs in numerous localities. Only the finest are mentioned here: Beautiful crystals occur in Tyrol, Austria, and huge examples come from Bologna and Pavia, Italy. The Sicilian Sulfur mines in Italy have produced crystal clear specimens with bright-yellow Sulfur inclusions. Gypsum "Desert Roses" occur in a number of places in the Sahara Desert in Africa. Fragile, acicular bunches occur in Whyalla, South Australia, and green, grass-like "mats" in Pernatty Lagoon, South Australia. Many fine localities also exist in North America.In Niaca, Chihuahua, Mexico, a cavern in the Maravilla Mine (dubbed "cave of the swords" because of the gigantic crystals found there) has produced magnificent, enormous, perfect crystals. In Nova Scotia, Canada, a large Gypsum deposit formed by altered Anhydrite is noted for individual crystal masses where expansion from the hydration is apparent. Gypsum "Desert Roses" occur in abundance in Alfalfa Co., Oklahoma. Stand-alone, perfect "floating" crystals are found in clay at Ellsworth, Mahoning Co., Ohio. Huge crystals were obtained from a cave in South Wash, Wayne Co., Utah. Severely curved Gypsum crystals and "Gypsum Flowers" come from the famous Mammoth Caves of Kentucky, and lustrous crystals have come from Lockport, Niagara Co., New York. Many states contain large deposits that stretch over large regions. Such deposits exist in New York, Ohio, Kentucky, Maryland, Tennessee, Iowa, Michigan, Texas, New Mexico, Arizona, and California.


Question and answers:

1. What is gypsum?
A. Gypsum is one of the most common minerals in sedimentary environments. Its chemical formula is Ca(SO4).2H2O.

2. What are the different varieties of gypsum?
A. Selenite, satin spar, Alabaster, Desert rose.

3 What are the industrial uses of gypsum?
A. Plaster, wall board, some cements, fertilizer, paint filler, ornamental, etc.

4. What are the properties of gypsum?
A. Gypsum is colourless to white. Sometime it is tan, blue, pink, reddish brown to grey.
Its crystal habit is massive, flat, elongated.
Its specific gravity is 2.31 – 2.4. Its hardness is 1.5 – 2.

5.What are the associated minerals of gypsum?
A. Calcite, sulphur, Halite and borax.

6. What is the crystal system of graphite?
A. It is monoclinic 2/m, prismatic.
 

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