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Feldspar & Pegmatite

What is feldspar?

Imerys feldspar

Feldspar is the name given to a group of naturally occurring alumino-silicate minerals containing varying amounts of potassium, sodium, calcium and/or lithium. The feldspar group of minerals is by far the most abundant group of minerals in the Earth’s crust, making up about 50% of all rocks. 


Feldspar minerals are essential components in igneous, metamorphic and sedimentary rocks, to such an extent that the classification of a number of rocks is based on their feldspar content. Although highly present in igneous rocks like granite, commercial feldspar is generally mined from pegmatite or feldspathic sand deposits. Pegmatites are rocks composed of several minerals — usually potassium feldspar, quartz and kaolin.

Physical properties

Imerys feldspar
  • High alumina and alkali content

  • High potassium content

  • Low iron content

  • Chemical inertness

  • pH stable

  • Consistent hardness (6-6.5 on Mohs scale)

  • Ceramics
  • Glassmaking
  • Ceramics

    Used in ceramics, feldspar and pegmatite are the main vitrifying or fluxing agent used during the firing process of ceramic bodies. Feldspars with low levels of colored oxides are particularly prized for white tableware and sanitaryware production.

  • Glassmaking

    In glassmaking, Imerys feldspars are excellent fluxing agents for flat and container glass, as well as for insulation wools. Feldspar is an excellent source of alumina which improves end product hardness, durability, and resistance to chemical corrosion.

For more information, please visit Imerys Ceramics.