What Is Potassium Feldspar, And How Is It Formed?

 Potassium feldspar is a common variety of silicate minerals formed under such conditions of low temperature, relatively high pressure, and the most commonly known being from the end product of volcanic eruption. This mineral can be found in areas that experienced gneiss formation. It has also been known to form because of the metamorphism of potassium-rich mica or where feldspars are abundant and it can form beyond the hydrosphere within planets and moons. Potassium Feldspar is usually seen in granite formations. Potassium Feldspar is a silicate belonging to the same family as quartz and feldspars, with compositions KAlSi3O8 to KAlSi4O10. It is also called orthoclase or alkali feldspar and is one of the most common rock-forming minerals on earth.

Formation of potassium feldspar

Two ways are there by which potassium feldspar can be formed. The first method involves the process of crystallization from magma. The second way involves contact metamorphism at high temperatures and pressures. The formation of potassium feldspar takes place at a lower temperature than that required for sodium feldspars. This explains why sodium feldspars are usually found in igneous rocks, while potassium feldspars are usually found in sedimentary or low-grade metamorphic rocks. Potassium feldspar is chemically stable in contact with magma because it does not contain any water, so it can form at depth where temperatures are high but pressures are low. It tends to crystallize out of melts more readily than other types of feldspar because its melting point is much lower than that of quartz, which is normally the last mineral to crystallize out of a melt (see Bowen's Reaction Series).

Characteristics of Potassium Feldspar

Potassium feldspar is a monoclinic mineral with a chemical composition of KAISi3O8 or KAISi4O10 or K2O*Al2O3*6SiO2. The main components are silica (SiO2), and alumina (Al2O3). Potassium feldspar has a white to clear color with no banding (patterns). It has a hardness of 6 on the Mohs scale (the hardness of quartz is also 6). It has a vitreous luster and can be found in many different colors. The name "potassium" comes from the Latin word "potis", which means "pot". Potassium feldspar, also known as K-feldspar, is a potassium-rich alkali metal silicate mineral. It is white or white in powder form, glassy or translucent. Potassium feldspar has a low melting point and good fluidity. It can be used as a flux to lower the melting point of the glass batch and improve the quality of glass products. The crystals are mostly tabular or blocky, often with surface grooves or striations. The color is mostly white or light gray; sometimes it is also red, green, yellow, and brown due to the presence of iron.

Where can potassium feldspar be found?

Potassium feldspars are widespread minerals; they are mainly found in igneous rocks with a higher silica content, such as granite, porphyry, diorite, and syenite; in some regionally metamorphosed rocks; and also in a variety of sedimentary rocks ranging from sandstone to limestone. Potassium feldspar is found in both massive forms (granites) and as crystals, associated with plagioclase feldspar. Lava flows also contain potassium feldspar and has been used as raw material to make cement. Feldspars are extensively used in the production of glass and ceramics because of their optical properties.

Uses of potassium feldspar

Potassium feldspars have applications in many different fields, for example, they are used to make ceramic glaze, dinnerware, and pottery. They are also used as fillers for paints, plastics, and rubber. Used as raw materials for the production of potash fertilizer, potassium sulfate, and potassium chloride and also used for porcelain making.

Classification of potassium feldspar

According to the characteristics of potassium feldspar can be classified into three types: 


Orthoclase(KAlSi3O8) is the most important feldspar. It is a transparent mineral with a glass luster, and its hardness reaches 6. The ratio of potassium and sodium in orthoclase is 1:0, and its composition contains no sodium.  Potassium feldspar is white or gray and sometimes has a pink or light yellow color. The mineral luster is glassy and it has an orthorhombic crystal system.

Microcline (KAlSi3O8)

Microcline (KAlSi3O8) has a vitreous luster and a triclinic crystal system. Its hardness is 6 and its density is 2.56-2.58g/cm3. Microcline is mainly distributed in the United States, Brazil, and India. Microcline is a type of potassium feldspar that is more common and stable than orthoclase. It is also characterized by its white color but has a triclinic crystal system.

Albite (NaAlSi3O8)

The albite (NaAlSi3O8) has an earthy luster and belongs to the cubic crystal system. The albite has two classifications: oligoclase and albite-oligoclase. The oligoclase (NaAlSi3O8) color is white, grayish-white, or light blue, sometimes there are black spots after weathering. Albite is the most common type of feldspar in the earth’s crust. It has a white-to-gray color and is characterized by its perfect cleavage feature and glassy luster. 


Potassium feldspar is a group of plagioclase feldspars that have a high potassium content. Potassium feldspar is made up of nearly 60% of potassium. The mineral also contains silica and alumina. The presence of potassium in this rock gives the crystals a bright color. It is transparent when to cut into slabs but has a translucent appearance when it remains in its solid form. When formed, potassium feldspar crystals grow relatively large compared to other types of plagioclase. But its uses are few. Potassium feldspar is mainly used in the ceramics industry and as an abrasive. 

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