Feldspar

(KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8)

Properties

Chemical Properties - Potassium, Silicon, Sodium, Calcium, and Aluminum

Physical Properties - Feldspars typically have a luster ranging from glassy to pearly. It also has a hardness of 6, which is harder than glass.

Feldspar is an abundant rock-forming mineral typically occurring as colorless or pale-colored crystals and consisting of aluminosilicates of potassium, sodium, and calcium.

Where is it? How do we get it?

The United States produces about $45 million worth of feldspar annually. North Carolina generates nearly half of the raw feldspar produced in the United States. Six other states produce smaller amounts. Other countries producing feldspar include Brazil, Colombia, France, Germany, India, Mexico, Norway and Spain.

How is it extracted and mined?

In Virginia, anorthosite is an igneous rock consisting of predominantly plagioclase feldspar with minor amounts of pyroxene, olivine, and iron oxides. The feldspar-rich rock is extracted using open pit methods, then crushed, classified and dried on-site. Heavy minerals are removed from the material by electrostatic and magnetic processes. The processed material is then transported by truck and rail to markets.


  1. Conventional open-pit mining methods including removal of overburden, drilling and blasting, loading, and transport by trucks are used to mine ores containing feldspar. A froth flotation process is used for most feldspar ore beneficiation.
  • Open pit mining is a surface mining technique of extracting rock or minerals from the earth by their removal from an open pit or borrow. Open-pit mines are used when deposits of commercially useful minerals or rock are found near the surface.
  1. The ore is crushed by primary and secondary crushers and ground by jaw crushers, cone crushers, and rod mills until it is reduced to less than 841 µm (20 mesh). Then the ore passes to a three-stage, acid-circuit flotation process.
  2. An amine collector that floats off and removes mica is used in the first flotation step. Also, sulfuric acid, pine oil, and fuel oil are added. After the feed is dewatered in a classifier or cyclone to remove reagents, sulfuric acid is added to lower the pH. Petroleum sulfonate (mahogany soap) is used to remove iron-bearing minerals. To finish the flotation process, the discharge from the second flotation step is dewatered again, and a cationic amine is used for collection as the feldspar is floated away from quartz in an environment of hydrofluoric acid (pH of 2.5 to 3.0).

How is it sold?

In the US, $100 - $500 per metric ton( wholesale)

Uses Then and Now

Feldspars have always been used widely in the glass and ceramics industries. Alkali feldspars are more commonly used commercially than plagioclase feldspars. Albite, or soda spar as it is known commercially, is used in ceramics. In addition, several feldspars are used as gemstones. For example, varieties that show opalescence are sold as moonstones. Spectrolite is a trade name for labradorite with strong colour flashes. Sunstone (oligoclase or orthoclase) is typically yellow to orange to brown with a golden sheen; this effect appears to be due to reflections from inclusions of red hematite. Amazonite, a green variety of microcline, is used as an ornamental material.

How is the Environment affected?

Feldspar itself doesn't upset nature, as it makes up 60% of the Earth 's crust, but the mining does. All the machines and chemicals used are constantly being added to the atmosphere. The digging and drilling has also caused deforestation.