Feldspar: Composition, Structure, Types, Usage, Substitute

Feldspar is a group of minerals that consists of alumina and silica in their chemical makeup. Feldspar is a natural mineral. They can also be described as a group of rock-forming silicate minerals. It is one of the most common mineral groups and forms about 60% of rocks, clay, sand. And various other unconsolidated sediments. They are an integral part of rock classification schemes. Orthoclase, plagioclase feldspars, microcline, etc., are members of feldspar. Here we will learn more about Feldspar, its composition, structure, etc.

Key Takeaways: Feldspar, Natural Minerals, Orthoclase, Alumina, Silica

Read More: Number of Moles Formula

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Feldspar Chemical Formula

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• Potassium feldspar chemical formula or (K-spar) formula- KAlSi₃O₈
• Sodium feldspar chemical formula or albite formula- NaAlSi₃O₈
• Calcium feldspar chemical formula- CaAl₂Si₂O₈

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Properties of Feldspar

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• Feldspar's chemical formula depends on its composition. Each chemical formula has a different composition. The specific chemical formula is KAlSi₃O₈ – NaAlSi₃O₈ – CaAl₂Si₂O₈
• The minerals have a constant pH value and are chemically alert.
• As per the physical properties of Feldspar, it has a monoclinic or triclinic crystal system. The refractive index of this mineral is 1.518 - 1.526. 
• Feldspar has two cleavages that contain two planes that intersect each other at an angle of 90º. 
• The density of Feldspar is 2.56g/cm³.
• According to the Mohs hardness scale, the hardness of Feldspar is 6 - 6.5.

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Feldspar Composition

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Silicate minerals, also known as tectosilicates are a type of natural mineral. Silicon ions are joined by shared oxygen ions that form a three-dimensional network. Three endmembers define the compositions of major elements in common feldspar. 

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Feldspar Structure

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Feldspar crystal's backbone is made up of aluminosilicate tetrahedra. In each tetrahedron, an aluminum, also known as silicon ion, is enclosed by four oxygen ions. This forms a three-dimensional network when each oxygen ion is shared by tetrahedra.

In feldspar, long chains of aluminum silicate tetrahedra are present, called crankshaft chains due to their kinked form. Each crankshaft chain forms a three-dimensional network by fusing four-membered rings connected to the chains. The structure of the feldspar is open for cations (calcium, potassium, and sodium) so that they can fit inside and balance the charge. 

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Types of Feldspar

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There are two types of alkali feldspars: 

1. Containing potassium in combination with sodium, aluminum, or silicon.
2. Containing barium (barium replaced potassium). 

The first type includes:

• Orthoclase (monoclinic) KAlSi₃O₈
• Sanidine (monoclinic) (K, Na)AlSi₃O₈
• Microcline (triclinic), KAlSi₃O₈
• Anorthoclase (triclinic) (Na, K)AlSi₃O₈

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Uses of Feldspar

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• Bathroom tiles, construction tiles, dinnerware, etc. are all made of feldspar.
• Feldspar is also used in the manufacturing of glass and ceramics.
• Feldspar is used as a flux. Flux is used to decrease the melting temperature of a substance such as glass.

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Substitute of Feldspar

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There is numerous substances that can be used as a substitute for feldspar. Pyrophyllite, talc, quartz mixtures, clays, etc. are a few of the minerals that are substitutes for feldspar. In the near future, these substances' demand will decrease due to the abundance of feldspar. 

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Mining of Feldspar

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Top largest producer of feldspar is North Carolina, California, Idaho, Georgia etc. Feldspar is mined from gigantic granite bodies called plutons. The largest component of the Earth’s crust is feldspar thus it is believed that the supply of feldspar is sufficient enough to meet the demands for a long period of time. At present, the demand for raw feldspar is met by mines located all over the world. 

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Things to Remember

• 60% of Earth’s crust is made up of feldspar. Therefore, it is available in sufficient quantities.
• Feldspar is divided into two broad categories: aluminum and silica. 
• Italy, Turkey, and China are the largest producers of Feldspar. 
• The pH value of feldspar is constant and remains the same. 

Also Read: Natural Resources