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Home > Products > Minerals > Feldspar

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Uses

 

Feldspar is used to make dinnerware and bathroom and building tiles. 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.

Substitutes and Alternative Sources

Feldspar can be replaced by other minerals and mineral mixtures of similar physical properties. Minerals that could be used to replace feldspar include clays, talc, and feldspar-silica (quartz) mixtures. The abundance of feldspar will make these substitutions unnecessary for the foreseeable future.


 

Background

 

Feldspar is the mineral name given to a group of minerals distinguished by the presence of aluminum (Al) and the silica ion (SiO4) in their chemistry. This group includes aluminum silicates of soda (sodium oxide), potassium (potassium oxide), or lime (calcium oxide). Feldspar is the single most abundant mineral group on Earth. Together, the varieties of feldspar account for one half of the Earth’s crust. The minerals included in this group are orthoclase, microcline, and the plagioclase feldspars. They form in a variety of thermal environments, during the crystallization of liquid rock (magma), by metamorphism of rocks deep in the earth, and in sedimentary processes.

Feldspars are relatively hard at 6 on Moths' hardness scale. Feldspars are generally light-colored, including white, pink, tan, green, or gray. The color varies due to impurities within the crystal structure. Feldspar is the mineral that gives granite its pink, green or gray color.

When feldspar weathers from igneous or metamorphic rocks, it can accumulate as sand. It is, however, easily weathered, and eventually will break down into clay.


 

Name

The name feldspar is a contraction of the longer name feldspar, some early specimens were found in fields. The term spar is a generic term used by geologists to refer to any non-metallic mineral with a glassy (vitreous) luster that breaks on distinct flat surfaces (planes). The name was officially given its name by Johan Gottschalk Gallerias in 1747.

Sources

 

Feldspar is mined from large granite bodies, from pegmatite’s (formed when the last fluid stages of a crystallizing granite becomes concentrated in small liquid and vapor-rich pockets that allow the growth of extremely large crystals), and from sands composed mostly of feldspar.

Because feldspar is such a large component of the Earth’s crust, it is assumed that the supply of feldspar is more than adequate to meet demand for a very long time to come. It is so abundant that geologists and economists have not even compiled data on potential deposits of feldspar for future consumption. Present mines worldwide are adequately meeting the need for raw feldspar.

The United States produces about $45 million worth of feldspar annually. North Carolina generates nearly half of the raw feldspar produced in the Iran. Six other states produce smaller amounts. Other countries producing feldspar include Brazil and Colombia…


 

“Potash Feldspar In Ceramics”

“Potash Feldspar In Ceramics” In ceramic bodies, the main vitrifying (fluxing) agent is feldspar. The majority of white ware bodies contain acceptable proportion of feldspar. It acts as a flux. In the ceramic industry, the flux is defined as that portion of the body which develops glass phase. This is provided mostly by feldspar. The amount of flux in a ceramic body should be only in such a proportion as to develop the desired amount of vitrification. If excess of flux is added, the fired body becomes very glassy and consequently, will be also brittle. Potash feldspar is generally used in Ceramics, Glass, and Electrodes. The glass and ceramic industries are the major consumers of feldspar and takes 95% of the total consumption.

“Chemical Composition of Feldspars”:

All the rock-forming feldspars are aluminosilicate minerals with the general formula AT4O8 in which A = potassium, sodium, or calcium (Ca); and T = silicon (Si) and aluminum (Al), with a Si:Al ratio ranging from 3:1 to 1:1. Microcline and orthoclase are potassium feldspars (KAlSi3O8), usually designated Or in discussions involving their end-member composition. Albite (NaAlSi3O8—usually designated Ab) and anorthite (CaAl2Si2O8—An) are end-members of the plagioclase series. Sanidine, anorthoclase, and the perthites are alkali feldspars whose chemical compositions lie between Or and Ab. As is apparent from the preceding statements, solid solution plays an important role in the rock-making feldspars. (Members of solid-solution series are single crystalline phases whose chemical compositions are intermediate to those of two or more end-members.) The alkali (Or-Ab) series exhibits complete solid solution at high temperatures but only incomplete solid solution at low temperatures; substitution of potassium for sodium is involved. The plagioclase (Ab-An) series exhibits essentially complete solid solution at both high and low temperatures; coupled substitution of sodium and silicon by calcium and aluminum occurs. The An-Or system has only limited solid-solution tendencies. Many perthites are formed when high-temperature potassium-sodium feldspars of appropriate compositions are cooled in such a manner that the original solid-solution phase exsolves (i.e., unmixed, so that a homogeneous mineral separates into two or more different minerals) to form intermixtures—sometimes termed intergrowths—of two phases. Many elements other than those required for the Or, Ab, and An end-member compositions have been recorded in analyses of feldspars. Those that have been recorded to occur as substitutions within the feldspar structures include lithium (Li), rubidium (Rb), cesium (Cs), magnesium (Mg), strontium (Sr), barium (Ba), yttrium (Y), ferrous iron (Fe2+), thallium (Tl), lead (Pb), lanthanum (La) and other rare earth elements, and ammonium (NH4) in the A position; and titanium (Ti), ferric (Fe3+) and ferrous (Fe2+) iron, boron (B), gallium (Ga), germanium (Ge), and phosphorus (P) in the T position. Of these, substitution of some barium for potassium and some titanium or ferric iron or both for aluminum are especially common in alkali feldspars. Several other elements also have been recorded as traces in feldspar analyses; it seems very likely, however, that some of these elements may reside in impurities—i.e., within unrecognized microscopic or submicroscopic inclusions of other minerals