Potassium feldspar is one of the most abundant minerals on the Earths crust and it is an essential part of many igneous rocks. It is composed primarily of potassium, sodium, calcium and aluminum, with a relative abundance of silicates which play a major role in the formation of feldspars. Potassium feldspar is most abundant when it occurs in a large volume. It is commonly found in association with other minerals such as quartz, biotite, or pyroxene.
Potassium feldspar occurs naturally in a large range of colors, depending upon the trace mineral impurities that are present. It may range from almost colorless to shades of pink, yellow, brown, green, or black and may be sparkly or dull, depending on its composition and crystal structure. Through the alteration and oxidation of the feldspar, different colors are inhibited after heating.
Potassium feldspar is used extensively in the ceramic and glass industry. It is a source of potassium oxide which is used as a flux and in glaze frits. Potassium feldspars are also used as fillers in plastic and rubber. The low index of refraction and the low dispersion of visible light renders them suitable for use in some optical applications.
In geological applications potassium feldspar is a common subordinate mineral within igneous rocks such as granite or syenite. It occurs in amounts from 5 to 10%, but because it is easily altered it is rarely the dominant mineral within the rock. Potassium feldspars are important constituents of volcanic rocks and are also found within many sedimentary rocks.
Potassium feldspar has been used as a gemstone since antiquity, when it was known as amazonstone, moonstone and sunstone by the Greeks. Nowadays it is mostly known as moonstone, although the name amazonstone is still used to describe some varieties. It is most commonly found in shades of green and yellow, although some blue and orange varieties have also been found. It is usually cut and polished as cabochons and is most valuable when the cut reveals a large or multicolored eye when lit from behind.
In conclusion, potassium feldspar is one of the most abundant minerals on the Earths crust and one of the most versatile. It has a wide range of applications, from ceramics and glass, to engineering and gemstones. With an immense variety of colors, sizes and uses, this mineral holds a great potential to be used in a large array of industries.
