Gypsum mineral raw material – gypsum, anhydrite and gypsum-containing rocks
Samara plant "Strommashina", being a producer of equipment for production of gypsum materials sets out the main data on natural gypsum raw material. The main source of raw material for production of gypsum materials and items is natural fields of gypsum and anhydrite as well as the fields of gypsum-containing rocks in a certain extent. Besides, gypsum-containing rejects of some ranges of productions (phosphogypsum, acid fluoride, titanium gypsum, vitamin gypsum, borogypsum and others) shall be considered as a perspective raw material for getting gypsum binding materials.
Natural gypsum raw material.
Gypsum, anhydrite and и gypsum-containing rocks.
Natural gypsum and anhydrite are practically monomineral rocks, each of them consists of homonymous minerals (gypsum or anhydrite), usually with some extent of quartz, carbonate, clay material, less frequently bituminous material, pyrites, etc. Generally gypsum and anhydrite deposits in the earth shell exist jointly.
Gypsum refers to sulphate class and is represented by calcium sulfate dihydrate. Except crystallization water, gypsum has hygroscopic moisture that is on the surface of gypsum rock and in its pores. Crystal gypsum in monoclinic system, crystals are plate-like, columnar, needle-shaped and fibrous. Crystals have extremely perfect cleavage on symmetry plane on which they are expanding on plain shiny plates, as for other directions - cleavage is less perfect.
Hemihydrate plaster is colorless and transparent however usually in connection with contamination has a grey, yellowish, pink, brown, sometimes black color. Shine is glassy, breaking is hackly.
Gypsum is distinguished according to its structure:
- Grainy compact gypsum with sugary grained breaking sometimes called alabaster;
- Plated gypsum laying in type of flat transparent crystals, called gypsum spat;
- fine-fibrous gypsum with silk gloss mounted from regularly spaced crystals called selenite.
Anhydrite relates to sulphate class and is waterless calcium sulfate. Anhydrite is crystallized in orthorhombic system usually in a form of small crystals of prismatic or cube-shaped form; it has perfect cleavage on three orthogonally related directions. Usually it is seen in a form of earthy, less frequently fibrous aggregates.
Color – white, grey, less frequently blue, pink or dark grey. Shine is glassy, breaking is wavy. It absorbs water slowly in moist environment and passes into gypsum.
Physicotechnical properties of gypsum and anhydrite
|true density, g/cm3||2,32||2,89|
|Breaking strength , MPa:
Gypsum containing rocks are the mixture of small gypsum crystals with clay sand and carbonic material. These rocks are known under various names: clay gypsum, friable gypsum, etc. All those rocks on its structure are the finely dispersed mechanical mixture or friable, poorly cemented formation of grey, yellow or brown colors. Over 80% of material is represented by particles of size less than 0,01 mm. Real density of material is about 2 g/cm3, Mohs' hardness less than 1.
Gypsum materials and items (production and application). Reference book.
Under general editorship of A.V.Ferronskaya. – M.: Publishing house АСВ, 488 p.