Feldspar is by far the most abundant mineral group in the Earth’s crust, accounting for approximately 60% of terrestrial rocks. Most deposits offer albite as well as potassium and mixed feldspar. Chemically, feldspar is a silicate of aluminum containing sodium, potassium, iron, calcium or barium, or a combination of these elements. Feldspar is used to make most of the products we use every day: drinking glasses, protective glass, insulating fiberglass, floor tiles and shower trays in bathrooms, and tableware on which we eat. Feldspar is part of our everyday life.
Feldspar minerals are important components of igneous, metamorphic, and sedimentary rocks, and many rocks are classified according to their feldspar content. The mineral composition of most feldspars can be represented by the ternary system of orthoclase, albite, and anorthite. Chemically, feldspar is an aluminosilicate containing sodium, potassium, iron, calcium, barium, or a combination of these elements. The mineral whose composition is between albite and anorthite is called plagioclase, and the mineral between albite and orthoclase is called alkali feldspar. The latter category is of particular interest with regard to the industrial uses of feldspars.
Of the many rocks in which they occur, feldspars are especially abundant in igneous rocks such as granite, which contain as much as 50 or 70 percent alkaline feldspars. However, due to the presence of feldspar, granite is rarely used. Instead, a series of rocks that are geologically connected to granite is used. Most often, commercial feldspar is mined from pegmatite or feldspar placer deposits. Aplite is a fine-grained igneous rock that has the same mineral composition as granite and is often mined for its feldspar content. Basically, the two properties that make feldspars useful for downstream industries are their alkali content and alumina content. Among these elements, we can distinguish three series: feldspar sand, pegmatite, and feldspar.