Magnesite


Magnesite is a magnesium carbonate, having a chemical formula MgCO3. Magnesium is the eighth most abundant element in the Earth's crust and can be found in 60 different minerals. Magnesite does not ordinarily form good crystals, but can make up a substantial portion of some rock types. It forms commonly from the alteration of magnesium-rich rocks during low grade metamorphism while they are in contact with carbonate-rich solutions. It belongs to the calcite group, a group of related carbonates that are isomorphous with one another. All members of the calcite group crystallize in the trigonal subdivision of the hexagonal system have perfect rhombohedral cleavage, and exhibit a strong double refraction in transparent rhombohedrons. The most common form of Magnesite is white, microcrystalline, porous masses that are dull in luster, and have the appearance of unglazed porcelain. Because they are porous, they adhere to the tongue when licked. Many of the properties of magnesite are either identical or similar to those of calcite. However, the magnesium ion does not allow the carbonate ion (CO3) to interact as easily with cold acids, as the calcium ion does in calcite. This provides the best means of distinguishing magnesite from calcite. However, dolomite(MgCa(CO3)2) can be almost indistinguishable from magnesite.

Occurrence and deposits

Magnesite occurs as veins in and an alteration product of ultramafic rocks, serpentinite and other magnesium rich rock types in both contact and regional metamorphic terranes. These magnesites often are cryptocrystalline and contain silica as opal or chert. Magnesite is formed via carbonation of olivine in the presence of water and carbon dioxide, and is favored at moderate temperatures and pressures typical of greenschist facies. Magnesite can also be formed from metasomatism in skarn deposits, in dolomitic limestones, associated with wollastonite, periclase, and talc Magnesite is found in the region of Oberndorf, Styria, Austria, and in St. Gotthard, Zillertal, Austria. It is also available abundantly in countries like Korea, China, Brazil, Bahia, USA and many other European countries. In USA it exist on the west coast of Ranges of California.

Physical Properties
  • Color is white or gray, also tinted yellow or brown.
  • Crystal System is trigonal; bar 3 2/m.
  • Crystal Habits are usually massive forms such as lamellar, fiberous and course to fine grained rocks. Crystals are extremely rare, but when found are in the form of rhombohedrons or hexagonal prisms with a pinacoid termination.
  • Cleavage is perfect in three directions forming rhombohedrons.
  • Luster is vitreous.
  • Transparency crystals are translucent to transparent only in individual crystals.
  • Hardness is 3-3.5.
  • Specific Gravity is 3 to 3.3.
  • Streak is white.
  • Fracture is conchoidal to uneven.

Application/ uses

  • Magnesite has large application in Caustic-calcined magnesia where it is used in the Extraction of magnesium,Production of fused magnesia, Cement, Insulation, Paper, Fertilizer and animal feed.
  • As Brucite or magnesium hydroxide in Sugar refining,Flame and smoke retardants, Pharmaceuticals.
  • As Magnesium chloride in Cement, Ceramics and refractories, Textiles, and Paper.
  • As Magnesium sulfate in Pulp and paper,Animal feed, Pharmaceuticals
  • Magnesite can be used as a slag former in steelmaking furnaces, in conjunction with lime, in order to protect the magnesium oxide lining.
  • Magnesite can also be used as a binder in flooring material.

Question and Answer

  1. How does magnesite is differentiated with calcite?
Ans. Magnesium ion does not allow the carbonate ion (CO3) to interact as easily with cold acids, as the calcium ion does in calcite. By this method we can identify the magnesite.
  1. Where is the occurrence of magnesite seen?
Ans. Magnesite occurs as veins in and an alteration product of ultramafic rocks, serpentinite and other magnesium rich rock types in both contact and regional metamorphic terranes.
  1. Mention few properties of magnesite?
Ans.
  • Color is white or gray, also tinted yellow or brown.
  • Crystal System is trigonal; bar 3 2/m.
  • Hardness is 3-3.5.
  • Specific Gravity is 3 to 3.3.
  • Streak is white.
  1. What are the applications of magnesite?
Ans.
  • Magnesite has large application in Caustic-calcined magnesia where it is used in the Extraction of magnesium,Production of fused magnesia, Cement, Insulation, Paper, Fertilizer and animal feed.
  • As Brucite or magnesium hydroxide in Sugar refining,Flame and smoke retardants, Pharmaceuticals.
  • As Magnesium chloride in Cement, Ceramics and refractories, Textiles, and Paper.
References: www.wikipedia.com www.mineralzone.com www.galleries.com

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