The Feldspar Group (K,Na,Ca)AlSi3O8

The density of this mineral is 2600-2800 kg/m3

Feldspars are one of the most important groups of minerals in planetary sciences and by far the most common mineral in terrestrial surface rocks, making up about 60% of the crustal materials. They are what is known as "aluminum silicates", which means, as seen in the formula, that the foundation of the mineral is aluminum (Al) and siica (Si) with a cariable admixture of potassium (K), sodium (Na), or calcium (Ca).

The formula shows how K, Na, or Ca may substitute for each other in the aluminum.silicate lattice, providing a range of compositions known as the solid solution phenomenon. Because feldspars are so common there are two (really three) sub-classes:

How do feldspars relate to the magma chamber?
One important property of feldspars is that they are among the lowest-density silicate minerals. The density of about 2700 km/m3 constrasts with that of 3300 to 4300 kg/m3 for common volcanic silicate minerals, such as olivine, spinel, and garnet, and even higher values such as 5200 kg/m3 for the iron rich mineral magnetite. A consequence is that feldspars tend to float in magmas and accumulate closer to planetary surfaces than do the denser minerals.

The feldspars form in a framework tetrahedra structure, which means that all tetrahedra share all four O-2 atom with adjacent tetrahedra. The result is a framework that extends infinitely in three dimensions. This framework is moderately resistant to weathering and metamorphism.


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The Feldspar Group (K,Na,Ca)AlSi3O8

The density of this mineral is 2600-2800 kg/m3

Feldspars are one of the most important groups of minerals in planetary sciences and by far the most common mineral in terrestrial surface rocks, making up about 60% of the crustal materials. They are what is known as "aluminum silicates", which means, as seen in the formula, that the foundation of the mineral is aluminum (Al) and silica (Si).

The formula shows how K, Na, or Ca may substitute for each other in the aluminum.silicate foundation, providing a range of compositions.

Because feldspars are so common there are two (really three) sub-classes:

How do feldspars relate to the magma chamber?
One important property of feldspars is that they are among the lowest-density silicate minerals. The density of about 2700 km/m3 constrasts with that of 3300 to 4300 kg/m3 for common volcanic silicate minerals, such as olivine, spinel, and garnet, and even higher values such as 5200 kg/m3 for the iron rich mineral magnetite. A consequence is that feldspars tend to float in magmas and accumulate closer to planetary surfaces than do the denser minerals.

The feldspars form a "framework tetrahedra" structure, which means that all tetrahedra share all four O-2 atom with adjacent tetrahedra. The result is a framework that extends infinitely in three dimensions. This framework is moderately resistant to weathering and metamorphism.


This is a view of the Earth.
Click on image for full size version (40K GIF)
Image from: NOAA

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The major types of minerals

Not applicable at this reading level.


This is a view of the Earth.
Click on image for full size version (40K GIF)
Image from: NOAA

Go to a listing of Rocks by mineral group



Last modified November 15, 1997 by the Windows Team

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