FELDSPAR

Pottery, enamel, and ceramic ware; glass; soaps; abrasive; bond for abrasive wheels; cements and concretes; insulating compositions; fertilizer; poultry grit; tarred roofing materials.

Feldspar is e xtensively used in scouring and cleaning compounds and for a window cleaner.

General name for a group of sodium, potassium, calcium, and barium aluminum silicates. Commercially, feldspar usually refers to the potassium feldspars with the formula KAlSi 3O8, usually with a little sodium. Noncombustible.

Toxic as fine-ground powder.

Feldspars, a group of silicate materials, are the most abundant minerals in the earth's crust. Feldspars have a structure in which (SiAl)O₄ tetrahedral is linked together with potassium, sodium and calcium. Occasionally, barium ions also occupy large spaces in the same framework. Commercially, feldspar usually refers to potassium feldspar with the formula KA1Si₃O₈. This feldspar has little sodium.
The chemical composition of feldspars may be expressed as combinations of (a) anorthite (CaAl₂Si₂O₈), (b) albite (NaAlSi₃O₈),（c) orthoclase (KAlSi₃O₈), and (d) celcian (BaAl₂Si₂O₈).
Feldspars form colorless, white or pink crystals with a hardness of 6 on the Mho's scale. They are used in pottery, cement and concrete, insulating compositions, fertilizers and glass.
Feldspars are subdivided into two groups. One of them is alkali feldspar (including microcline, orthoclase and sanidine) which has a significant amount of potassium, a smaller proportion of sodium and negligible calcium. The other group, namely plagioclase feldspar, varies in composition from pure sodium feldspar (albite) to pure calcium feldspar (anorthite) with negligible amounts of potassium.

Feldspars (Al₂O₃ and SiO₄ tetrahedra) constitute60% of the outer 13 to 17 km of the earth’scrust and are the most common mineral in crystallinerocks. Feldspars are aluminum silicatesof potassium, sodium, and calcium.
The importance of the many feldspars thatoccur so widely in igneous, metamorphic, andsome sedimentary rocks cannot be underestimated,especially from the viewpoint of apetrologist attempting to unravel Earth history.
With weathering, feldspars form commerciallyimportant clay materials. Economically.feldspars are valued as raw material for theceramic and glass industries, as fluxes in ironsmelting, and as constituents of scouring powders.Occasionally, their luster or colors qualifythem as semiprecious gemstones. Some decorativebuilding and monument stones are predominantlycomposed of weather-resistantfeldspars.
Knowledge of the composition of a feldsparand its crystal structure is indispensable to anunderstanding of its properties. However, it isthe distribution of the aluminum and siliconatoms among the available tetrahedral sites ineach chemical species that is essential to a completeclassification scheme, and is of greatimportance in unraveling clues to the crystallizationand thermal history of many igneous andmetamorphic rocks.