Potassium Feldspar

Ceramic and Glass Applications

Potassium feldspar is commonly used as a flux in glassmaking and ceramics. Flux is a material that’s added to a solid to lower the solid’s melting point. The flux is a vital component of most glass and ceramic production because it helps control the viscosity of the glass and helps create a glassy phase in ceramics at low temperatures. This action lowers production costs significantly. The abundance of potassium feldspar makes it a logical and cost-effective choice for this application. In glassmaking, the alumina in feldspar also lends itself to the hardness, durability, and chemical resistance of the finished product.

  • Improves the hardness and durability of glass and ceramics
  • Improves the optical qualities of glass
  • Used in flat and architectural glassmaking
  • Great source of alumina in glazes
  • Increases chemical resistance of glass, ceramics, and other produced materials

 

Specifications

Potassium feldspar, also known as k-feldspar, is a silicate mineral with the chemical formula KAlSi308. It has a triclinic or monoclinic crystal system and a white streak, although the colour of the rock itself can be white, pink, grey, or brown. Its lustre is vitreous or glassy and it displays an uneven or conchoidal fracture pattern. Potassium feldspar scores between 6 and 6.5 on the Mohs hardness scale with an absolute hardness score of 72.

  • Colourless or very lightly coloured
  • Crystalline mineral structure
  • Melts well at medium to high temperatures (between 600° C and 750° C)
  • Includes orthoclase, microcline, and plagioclase feldspars

 

General information

Feldspar is a light or colourless, crystalline, tectosilicate rock mineral and is the most common mineral on Earth, making up more than 60% of the Earth’s crust. This is because feldspar is formed by the cooling of magma, and the temperature, pressure, and other elements within the magmas are favourable to its formation.

Feldspar refers to a group of minerals that are distinguished by the existence of alumina and silica within their chemistry. It is found in igneous, metamorphic, and sedimentary rocks and consists of aluminosilicates of potassium, sodium, and calcium. Surprisingly, feldspar has a hand in the majority of the products we come into contact with every day. Various types of glass, including fibreglass, floor and wall tiles in bathrooms and kitchens, and tableware are all examples of common products that require the use of feldspar during the manufacturing process.

The structure of feldspar is such that it can facilitate the presence of many other elements. It is generally mined from large bodies of granite, pegmatites, and sands. Pegmatites are coarse, crystalline, igneous rocks that are formed during water-wet stages of magma cooling. Potassium feldspar is a prevalent component of granite, pegmatites, and other igneous rocks.

Powders are made by crushing the crystalline rocks that contain the feldspar. These powders melt well at medium to high temperatures and are a cost-effective source of flux, which is any substance mixed with a solid to help lower its melting point. Feldspar is primarily used as a flux to promote vitrification in ceramics and glass. Vitrification is the conversion of a material into a non-crystalline, amorphous solid, or glass. When used in ceramics, this process makes the material impermeable to water.

Although deposits around the world vary widely and contain numerous impurities, and there is even disparity between occurrences of potassium feldspar specifically, producers are generally able to produce potassium feldspar that performs well in an assortment of applications.

Other common applications for potassium feldspar include paints, plastics, and rubber. As a filler, extender, and glaze in these industries, feldspar offers good dispersibility, chemical inertness, a stable pH, abrasion-resistance, frosting-resistance, and low viscosity. It’s also used in large quantities in the cement and asphalt industries as an aggregate and is used to make decorative building stones. Feldspar is also commonly used in the manufacture of enamel and scouring powder and is fundamental to the fertilizer and agriculture industries as a reliable source of potassium salt with distinct social and economic benefits.

Other types of feldspar include the sodium endmember, albite feldspar. This is a pure white feldspar that contains less than 10% anorthite. Another is anorthite feldspar, which is the calcium endmember. Anorthite is found in mafic igneous rocks and is most common on the moon, but rarely found on Earth. Potassium feldspar is commonly found in large amounts in felsic igneous rocks.

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