Feldspars are a group of minerals that cover more than half (60%) of the Earth’s crust. They are formed when magma cools directly within the earth’s crust. The International Union of Geological Sciences categorizes feldspars into two broad mineral groups which are: potassium feldspars and plagioclase feldspars.

When feldspars weather, they form clay minerals and aluminum ores. These are among the most sought-after minerals in modern industries. In this article, we discuss the potassium feldspar mineral, its components, and occurrence in depth.

General Information about Potassium Feldspar

The term ‘Feldspar’ was coined from two German words ‘feld’ and ‘spar’ where the former means field while the latter means crystal. The name depicts the abundance of feldspar minerals in the earth’s crust.

Properties of Potassium Feldspar

Potassium feldspar falls in the group of aluminosilicate minerals which have a general formula of AT4O8, where A is potassium, T is silicon and aluminum. The silicon to aluminum ratio (Si: Al) ranges from 3:1 to 1:1.

K-feldspar contains a group of other minerals that share similar chemical composition but have different physical structures. They include Orthoclase, Sanidine, and Microline. Here are some of the common properties of potassium feldspar:

  • Alternative names-K-Feldspar, K-spar, Potassic Feldspar, alkali feldspar, potash feldspar.
  • Varieties: adularia, Barian feldspar, barium adularia, valencianite.
  • Hardness: 6 to 6.5 on the Mohs Hardness Scale.
  • Luster: vitreous luster.
  • Color: opaque shades of white, gray, and pink.


  • Orthoclase – can be either white or pink and occurs in potassium-laden volcanic rocks. It is monoclinic in nature.
  • Sanidine – is mostly colorless and occurs in felsic plutonic igneous or metamorphic rocks.
  • Microcline – can be white, pink or green. It is usually found in granite, pegmatites and low-temperature hydrothermal veins. Microline is triclinic.

These minerals possess hard blocky crystals. In addition to that, each crystal mass has a pair of cleavage whose faces meet at almost 90 degrees. Potassium feldspar (especially the Or and Ab series) maintain their full solid-solution state when exposed to high temperatures. However, at low temperatures, they form an incomplete solid solution.

Pure fragments of K-feldspar crystals usually form rectangular blocks with irregular ends. Another property of the feldspars is that they have a vitreous luster. Most crystals have color variations such as opaque shades of white, gray, and pink.

Potassium feldspar and plagioclase crystals are so similar that they may react to create crystals with thin alternating seams. This happens when hot potassium and sodium feldspars are cooled in a way that their solid solution phase ex-solves. (Homogeneous solutions of each feldspar separate to form an intergrowth of the two feldspars.) The resultant mineral is called perthite.

Perthite formation can also occur when some sodium-containing fluids (plagioclase feldspar) replaces potassium in its original potassium-feldspar compound.

Metaphysical Details about Potassium Feldspar

rough moonstone and cabbed moonstone

Moonstone (Image Source: GIA.edu)

Potassium Feldspar minerals are renowned for their intriguing opalescence. Moonstone, which is a perthite of sodium and potassium aluminosilicate, is characterized by an attractive silvery or bluish iridescence. For this reason, it applied in different aspects of history and folklore. For instance, moonstone was used to accent jewelry, talismans, and sacred objects.

People particularly from India and Rome had a common belief that Moonstone had fallen from the sky, thus associating it with the moon. It was therefore believed to have healing properties. People also used it in casting love spells and clairvoyance practices. To date, many people are still fascinated by the mineral’s beauty and mystical lore.

The orthoclase crystal found within the potassium feldspar group of minerals is also used today as a healing gem. It is said to provide ladies with a feminine goddess energy. These claims suggest that women with sexuality issues regarding self-esteem and self-awareness can seek refuge in an orthoclase crystal.

Potassium feldspar crystals have an energy that helps individuals to connect their inner self to get a better understanding of situations and problems. It also helps people to cut off old ties to trauma and challenges that are impeding their development. These crystals have therefore found usage in chakra areas where solar plexus and heart chakras occur.

Application of K-Feldspar in the Making of Jewelry

The major mineral components of potassium feldspar are amazonite, moonstone, and orthoclase. They have glass-like luster making them a valuable resource in the jewelry industry. Potassium feldspar crystals have a hardness score of 6 to 6.5 on the Mohs Hardness Scale. This makes them durable enough to be used in jewelry making.


bezel set gold fill moonstone jewelry

Image Source: Pinterest

Moonstone jewels cost from as little as $10 up to $300 depending on the quality of the crystal and its setting. Those that are accented with gold and silver will undoubtedly be more expensive than their plated or pewter counterparts. The Rare Sri Lankan moonstone jewelry costs over $1,000. You can find some moonstone accessories such as earrings, rings, pendants, and necklaces at Auntie’s Treasures or Novica Jewelry.


Amazonite silver earrings

Image Source: Pinterest

Amazonite potassium feldspar is also sought after in the jewelry industry for its unique sea-green luster. However, it can easily break when subjected to pressure. Some of the amazonite jewelry include Golden Sea Currents, Heaven, and Belles, which you can find at Novica Jewelry.

Where Can We Find Potassium Feldspar Today

Turkey ranked best in potassium feldspar production in the 21st century. The other main producers of the mineral are Italy and China. Potassium feldspar also occurs in felsic igneous rocks in the Upper Midwest. The top states in the U.S. producing feldspar are North Carolina, Virginia, California, Oklahoma, Idaho, Georgia, and South Dakota in that chronological order.

Since the mineral is found relatively close to the surface, it is mined through open-pit method. It is extracted from large granite bodies referred to as plutons. Potassium feldspar can also be obtained from pegmatites or underground pockets that are rich in vapor allowing the growth or huge mineral crystals. Its mining has little negative impacts on the environment.

Summing Up

These are the main properties, uses, and facts you need to know about potassium feldspar mineral. Being a profoundly abundant mineral, it can meet human needs for the next several decades. However, it can be substituted with other minerals like quartz and pyrophyllite.