The Mineral Of Feldspar
Feldspar
Feldspar is a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth’s crust. From the perspective of the gemstone world, it would seem like quartz is the most abundant mineral in the world. The many quartz varieties include citrine, amethyst, ametrine, chalcedony, aventurine, onyx, agate, tiger’s eye, smoky quartz and rose quartz.
But from the point of view of mineralogy, it is feldspar that is the most common mineral. Feldspar is a group of minerals distinguished by the presence of aluminum and the silica ion in their chemistry. This group includes aluminum silicates of sodium oxide, potassium oxide, or calcium oxide.
Feldspar is derived from the German Feld, “field”, and Spath, “a rock that does not contain ore”. “Feldspathic” refers to materials that contain feldspar. The alternate spelling, felspar, has now largely fallen out of use. The mineral was officially given its name by Johan Gottschalk Wallerius in 1747.
There are two main subgroups of feldspar that produce gem-quality material: the potassium feldspars and the plagioclases, a series that ranges from calcium to sodium feldspars. Among the well-known feldspar gemstones are moonstone, orthoclase, amazonite, andesine, labradorite and sunstone.