ceramic bowls made with feldspar on a shelf

Feldspar: Uses And Applications

Feldspar are a class of rock-forming tectosilicate minerals that contains calcium, potassium or sodium and makes up more than half of the earth’s core by weight. Its minerals are largely found in igneous, sedimentary and metamorphic rocks spread across different parts of the world. These minerals are such essential components of these rocks that the classification of a number of rocks is based on the feldspar mineral content.

For the most part, feldspars are naturally occurring in opaque shades of white to gray and pink to very dark grey and have other vitreous lusters. Since feldspars are made up of two split planes intersecting at 90degrees, parts of pure feldspar crystals have a huge tendency to form rectangular blocks with varying ends.

It is important to note that feldspars can be split into two primary groups which are potassium feldspars and plagioclase. Both forms of feldspars have two visible cleavages and a wealth of colors which overlap. Plagioclase, in particular, has small grooves on one of its cleavages which are commonly called striations.

ceramic pots that use feldspar in their creation
factory producing glass with feldspar

The mineral composition of most feldspars can be expressed in the ternary form including albite, orthoclase, and anorthite. The minerals of which composition is based primarily on the solid solution range between albrite and anorthite is what is known as the plagioclase feldspars while those between albrite and orthoclase or mono line are what is collectively known as alkali feldspars. They are referred to as alkali feldspars due to the presence of potassium and sodium minerals.

These alkali feldspars, especially alkali feldspars of potassium origin are of particular to industries because of its wide range of applications. They play pivotal roles in the production of fillers in the paint, rubber, adhesive and plastic industries. They are also used as fluxing agents in glass and ceramic applications.

In general, most of the products we use on a daily basis are made with feldspar. This includes floor tiles and shower basins bathrooms, glass for drinking water and other fluids, fiberglass used for insulation and different types of tableware used for dishing meals.

In fact, a number of popular gemstones like sunstone, moonstone, labradorite, spectrolite, and amazonite are feldspar minerals.

blue pigment

Physical Properties of Feldspar Minerals

Feldspar minerals have a surprisingly consistent range of physical properties common to them. Most of the minerals present in feldspar have two directions of perfect cleavage which intersect at nearly right-angles. Not only do they have about the same angle of inclination for their cleavages, but they also have similar Mohs hardness and specific gravity.

Most feldspar minerals have a specific gravity within the 2.5-2.8 range while their Mohs hardness hovers about 6 to 6.5. In addition to all these similarities in physical properties, all feldspar minerals have a vitreous luster that is mostly pearly on cluster faces. This is a great way of identifying feldspar minerals.

ceramic bowls made with feldspar

These properties of feldspar minerals which are mostly consistent in all forms of these minerals are pretty useful even when the feldspar crystals to be identified are very small. It is extremely easy for people who are conversant with feldspar cleavages to identify feldspar in igneous rocks. No matter how small the feldspar crystals are, they can be easily identified as separate from other minerals when an igneous rock is examined using a hand lens, as its properties are easy to identify.

With minimal practice, one can determine the Mohs hardness of even tiny feldspar minerals using a set of mineral hardness picks and a hand lens.

Uses and Applications of Alkali Feldspar

The most important properties of feldspar to downstream industries and many other industries are their alumina and alkali content. For this reason, alkali feldspars (potassium feldspars) have a wide range of applications in paint industries, glass, and ceramic making industries. Here are some of the applications of potassium feldspars.

Glass: Feldspar is a critical material in the production of glass. It is also a crucial raw material in its production as it tends to act as a fluxing catalyst. As a fluxing catalyst, it reduces the temperature of quartz while simultaneously helping to keep the viscosity of the produced glass at the right correct range. It is the alkali content of the feldspar that helps it function effectively as a flux in glass making.

Empty green glass wine bottles
glass making

Fillers: Feldspars are functionally used as extenders and fillers in paints, rubbers, and plastics. It is an effective filler because of a number of factors. These factors include its stable pH, high chemical inertness, good dispersibility, impressive refractive index, resistance to frosting, high resistance to abrasion and low viscosity at high filler loading. In general, the products used for such purposes are fine-milled grades.

feldspar pellets

Ceramics: Putting things in perspective, feldspar is considered the other most critical ingredient – besides clay – in the production of ceramics. It doesn’t have a definite melting temperature, as it melts slowly throughout various temperatures. This is one of its advantages as it accelerates the melting of clays and quartz, while simultaneously allowing modulation of this crucial stage in the production process. They are generally used as fluxing catalysts to produce a glassy coating at low temperatures. They are also used as a source of alumina and alkalis in glazes.

Most often than not, feldspars improve the toughness, durability, and strength of the ceramic body. Also, they melt, soften and wet other components of the batch mix.

ceramic bowls made with feldspar
ceramic cups made with feldspar

Enamel glazes: In enamel glazes, feldspar helps to enhance the aesthetics of the final product by ensuring that there are no errors in the final product. It is useful in the manufacturing of sanitary ware, ceramic tile glazes, tableware, giftware, electrical, and enamel frits. In sanitary wares, feldspars are used to facilitate the optimization process.

Feldspar also has a host of other end-uses which include urethane, mild abrasives, paints, welding of red coating, production of steel and latex foam.

glazed bowls

Other uses of Potassium Feldspar

Weathered potassium feldspars disintegrate into clay minerals and aluminum ores, both of which are important resources used in today’s society. These aluminum ores are collectively known as bauxite, a highly economically important mineral resource.

Welding: Potassium feldspars are very useful in the coating of welding electrodes due to their excellent fluxing properties. They are particularly used in the coating of electrodes used in the manual arc process, a process used for the welding ferrous alloys in general fabrication industries, shipbuilding, hard-facing and structural steelwork.

Abrasives: Along with magnesium oxide, magnesium chloride and other synthetic glue, feldspars are used as a bonding agent in the manufacture of wheels, abrasives, disc and various other shapes.

In large volumes, they are used as coarse aggregate in the production of asphalt and concrete. In addition, they are also used in the manufacture of enamel, scouring powder and glass.

Some classes of potassium feldspar also have economic and aesthetic values as gemstones. Some of these gemstones include moonstones and amazonstone.

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Special Feldspars

It is worthy of note to mention that there a number of feldspar minerals who do not clearly fall under the plagioclase or alkali group. Some of these feldspar minerals are used as gemstones. These gemstones include labradorite, sunstone, and moonstone. These three minerals are lauded for their unique optical phenomena.

When light strikes a moonstone, it produces a glow within known as adularescence, in sunstone, the light entering the gemstone reflects with a glittery flash known instead as aventurescence. In labradorites, light entering the gemstone is scattered, producing iridescent reflection. This, in turn, produces interesting lashes of strong iridescent colors like orange, yellow, green, electric blue, and pink. This phenomenon is referred to as labradorescence, a name coined from the mineral that produces such a phenomenon.

feldspar