Feldspars - Mining Fundamentals

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Feldspars are a group of silicate minerals that occur in igneous rocks. They are said to be one of the most abundant groups of minerals in the earth's crust. The group consists of about 20 members.

Silicon and oxygen form the major foundation for the group; however calcium, sodium, and potassium are also present. A key characteristic of Feldspars is that one of these elements is generally dominant, but a majority of the feldspars contain all three elements in varying amounts.

Feldspars are divided into two broad categories, as follows:

  • Plagioclase – scontain calcium and sodium; mostly found in mafic and intermediate rocks; occur in dark gray to black colors; a large number of them have striations
  • Orthoclase - contains potassium; mostly found in felsic igneous rocks; occur in pink or blue colors

The various types of plagioclase feldspars are listed below:

  • Albite
  • Andesine
  • Anorthite
  • Labradorite
  • Oligoclase
  • Bytownite

All feldspars have been known to have low symmetry. They tend to twin easily, and sometimes one crystal can even be twinned numerous times on a single plane, thereby producing parallel layers of twinned crystals. Their hardness is about 6 Mohs.

Feldspars have a dull to rarely vitreous luster, and the crystals are blocky in nature. Some feldspars can be triboluminescent. They tend to crystallize in igneous environments.


Feldspars play an important role in many applications, such as the following:

  • As fluxing agents in ceramics and glass applications
  • Used as functional fillers in the paint, plastic, rubber, and adhesive industries
  • Used as fillers and extenders in some applications, such as paints, plastics, and rubber
  • Used in enamel composition, thereby providing the neatness of the end product and ensuring the absence of defects in products, such as ceramic glazes, ceramic tile glazes, enamel frits, sanitary ware, electrical porcelain, table ware, and gift ware
  • Used in paint, mild abrasives, welding electrodes, urethane, latex foam, welding of rod coating, and road aggregate



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