Why is feldspar the most common mineral

The determining factor for the formation of these three minerals with a KAlSi 3 O 8 composition is temperature. Sanidine is the high-temperature form, orthoclase is the intermediate-temperature form, and microcline is the low-temperature form. Arkose is a sedimentary rock that forms from the weathering of feldspar-rich igneous and metamorphic rocks. In sedimentary deposits produced from the weathering of feldspar-bearing igneous and metamorphic rocks, feldspars are usually most abundant close to the source area.

Feldspars generally decline in abundance with distance from the source because during transport, they can be attacked by weathering and altered to clay minerals. In addition, their two directions of perfect cleavage make them vulnerable to mechanical weathering, which decreases their particle size and exposes a greater surface area to chemical weathering. Arkose is usually found immediately down gradient and close to the outcrops from which the feldspar grains were weathered.

Long transportation distances destroy the feldspar grains, and extended exposure to weathering converts the feldspars into clay minerals. Clay minerals are feldspar's other contribution to the sedimentary record.

They accumulate as mud or soil and often form sediments that become shales and mudrocks. Right-angle cleavage: One of the most diagnostic properties of feldspar is its two directions of cleavage that usually intersect at or close to ninety degrees. Although there are many feldspar minerals, they all share a tight range of physical properties that are surprisingly consistent. Most of them exhibit two directions of perfect cleavage that intersect at or close to ninety degrees.

An example of this type of cleavage can be seen in the accompanying photo. Most feldspar minerals have a Mohs hardness of approximately 6 to 6. They all have a vitreous luster that is often pearly on cleavage faces.

The accompanying table shows the generalized physical properties of the feldspar mineral group. These consistent properties of feldspar are extremely useful even when the feldspar crystals are very small. People who are familiar with feldspar cleavage can pick up an igneous rock that contains crystals of just a few millimeters in size, examine it with a hand lens , and easily differentiate the feldspars from other minerals in the rock. With minimal practice they can also use a set of mineral hardness picks and a hand lens to determine the Mohs hardness of such tiny grains.

There are many feldspar minerals beyond the plagioclase and alkali series. A list is given in Table 1. Some feldspar minerals are unusual and extremely rare. Here are a few examples:. Feldspar from the Moon: The "Genesis Rock" is one of the most famous rocks ever collected. Analysis revealed that it is made up almost entirely of anorthite, a plagioclase feldspar, and is approximately 4 billion years old.

Reporters covering the Apollo Mission started calling the specimen the "Genesis Rock" and the name stuck. Image by NASA. Feldspar has been discovered in other parts of our solar system.

Astronauts visiting the Moon during the Apollo Missions brought back many samples of rock that were rich in feldspar. Vesta meteorite: A transmitted light photomicrograph of a eucrite meteorite that has been attributed to Asteroid Vesta. This specimen is a basaltic eucrite that is rich in calcium-rich plagioclase.

NWA is made of cemented fragments of basalt, a rock that forms from rapidly cooled lava. The fragments within the meteorite are mostly feldspar and pyroxene. Feldspars in Soils: This map shows the distribution of feldspar group minerals in the A Horizon of United States soils.

Click the image to enlarge. About , metric tons of feldspar is produced each year in the United States.

Most of this feldspar is crushed into fine granules or powders and then consumed in factories that produce plate glass, ceramic tile, fiberglass insulation, paints, plastics, pottery, container glass and other products. Most of these products play an important role in commercial and residential construction, and the demand for feldspar is supported by the health of the construction industry. These locations produce enough feldspar to supply nearly all of the nation's consumption.

The resource available for future production is enormous. The only challenge is that the feldspar resource might not be located at a convenient distance from points of consumption. Aventurescent sunstone: Close-up photo of a sunstone cabochon, showing beautiful flashes of aventurescence caused by light reflecting from the copper platelet inclusions within the stone.

Blue labradorite: Photograph of a labradorite cabochon with an electric blue play-of-color. Several varieties of feldspar minerals are used as gemstones. Three of them, moonstone, sunstone, and labradorite, are known for their unique optical phenomena. Moonstone is a gem material that consists of microscopically thin and alternating layers of feldspar minerals of different compositions. When light enters a polished gemstone and encounters these layers, it is scattered in many directions.

This produces a glow within the gemstone known as adularescence. The glow appears to float slightly under the surface of the gem and moves as the source of illumination moves, as the angle of observation is changed, or as the gemstone is moved under the light. People enjoy this soft glow, especially when it has a striking color or the body color of the moonstone is pleasing.

Orthoclase is the most common feldspar mineral to host the adularescent phenomena; however, it is also known in albite, oligoclase and labradorite. Sunstone is a gem that contains tiny plate-shaped and highly reflective particles with a common orientation. When light enters the gemstone, it strikes these particles and they reflect it with a glittery flash known as aventurescence.

The particles might be tiny flakes of copper , hematite , mica or other reflective mineral. Labradorite and oligoclase are the feldspar minerals that most often have aventurescence.

In ceramics and glass production, feldspar is used as a flux. A flux is a material that lowers the melting temperature of another material, in this case, glass. Feldspar can be replaced by other minerals and mineral mixtures of similar physical properties. Minerals that could be used to replace feldspar include pyrophyllite, clays, talc, and feldspar-silica quartz mixtures. The abundance of feldspar will make these substitutions unnecessary for the foreseeable future. Feldspar is used to make dinnerware and bathroom and building tiles.

Skip to content Return to Minerals Database. The feldspar group has nearly 20 recognized members, but only nine of those are common. These may be divided into two types of feldspar: plagioclase and alkali. Each plagioclase grain is made up of stacks of thin crystal with their molecules arranged in opposite directions.

This causes the cleavage planes to have fine parallel line across them called striations. Another diagnostic feature is the feldspars colour range. In this case, the colour typically ranges from white to gray. The main feldspars in this grouping include:.

Plagioclase Feldspar and Hornblende. Road cut on highway East of Quadeville, Ontario. Unlike plagioclase, orthoclase does not have striations across its cleavage plane. Cleavage faces will appear smooth. Orthoclase also typically has a colour range between white and pink, which is different than that of plagioclase.

Feldspars which are in this grouping include:. Orthoclase Crystals. Goodsprings, Nevada. The feldspar group is very large and there are many different chemical formulas.

Before a feldspar can be used its chemical composition must be determined. Different feldspars will behave differently. Some uses for the feldspar family in general include:. Wood Cox Mine, Bancroft. Feldspar is an incredibly abundant mineral. It has been found on the moon and in some meteorites. Feldspars are found in the every section of the rock cycle.

Many feldspars are igneous as they commonly precipitate out in magma as it cools.