Feldspar

	Email		Print
	Bookmark		Link

Feldspar

Feldspars are a group of rock-forming tectosilicate mineral

Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
s which make up as much as 60% of the Earth

Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
's crust

Crust (geology)

In geology, a crust is the outermost solid shell of a planet or moon, which is chemically distinct from the underlying mantle . Crusts of Earth , our Moon, Mercury , Venus, and Mars have been generated largely by igneous processes, and these crusts are richer in incompatible elements than their respective mantle s....
.

Feldspars crystal

Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions....
lize from magma

Magma

Magma is molten Rock that is found beneath the surface of the Earth, and may also exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and gas bubbles....
in both intrusive and extrusive igneous rocks, as veins, and are also present in many types of metamorphic rock

Metamorphic rock

Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form"....
.

Discussion

Ask a question about 'Feldspar'

Start a new discussion about 'Feldspar'

Answer questions from other users

Full Discussion Forum

Encyclopedia

Feldspars are a group of rock-forming tectosilicate mineral

Mineral

Earth

Crust (geology)

Crystal

Magma

Metamorphic rock

Metamorphic rock is the result of the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form"....
. Rock formed entirely of plagioclase

Plagioclase

Plagioclase is a very important series of Silicate minerals minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series ....
feldspar (see below) is known as anorthosite

Anorthosite

Anorthosite is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar , and a minimal mafic component . Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present....
. Feldspars are also found in many types of sedimentary rock

Sedimentary rock

Sedimentary rock is one of the three main Rock types . Sedimentary rock is formed by deposition and consolidation of mineral and organic material and from precipitation of minerals from solution....
.

Etymology

Feldspar is derived from the German

German language

German is a West Germanic languages, thus related to and classified alongside English language and Dutch language. It is one of the world's world language and the most widely spoken mother tongue in the European Union....
Feld, field, and Spat, a rock

Rock (geology)

In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock....
that does not contain ore

Ore

An ore is a type of Rock that contains minerals such as gemstones and metals that can be extracted through mining and refined for use. Samples of ore in the form of exceptionally beautiful crystals, exotic layering visible when sectioned or polished or metallic presentations such as large nuggets or crystalline formations of metals suc...
. "Feldspathic" refers to materials that contain feldspar. The alternative spelling, felspar, has now largely fallen out of use.

Compositions

This group of minerals consists of framework or tectosilicate

Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
s. Compositions of major elements in common feldspars can be expressed in terms of three endmembers

Endmember (mineralogy)

An endmember in mineralogy is a mineral that is at the extreme end of a mineral series in terms of purity. Minerals often can be described as solid solutions with varying compositions of some chemical elements, rather than as substances with an exact chemical formula....
:

Potassium-Feldspar (K-spar)

Orthoclase

Orthoclase is an important Silicate minerals mineral which forms igneous rocks. The name is from the Greek language for "straight fracture," because its two cleavage planes are at right angles to each other....
endmember K

Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
Al

Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
Si

Silicon

Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. The atomic mass is 28.0855....
₃O

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
₈

Albite

Albite

Albite is a plagioclase feldspar mineral. It is the sodium Endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content....
endmember Na

Sodium

Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
Al

Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
Si

Silicon

Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. The atomic mass is 28.0855....
₃O

Oxygen

Anorthite

Anorthite is a compositional variety of plagioclase feldspar. Plagioclase is an abundant mineral in the Earth's Crust . The formula of pure anorthite is calciumAluminium2Silica2Oxygen8....
endmember Ca

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....
Al

Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
₂Si

Silicon

Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. The atomic mass is 28.0855....
₂O

Oxygen

Solid solution

Alkali feldspar

The alkali feldspar group are those feldspar minerals rich in the alkali Chemical element potassium and sodium. The alkali feldspars include: albite, anorthoclase, microcline, orthoclase and sanidine....
. Solid solutions between albite and anorthite are called plagioclase
Plagioclase

Plagioclase is a very important series of Silicate minerals minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series ....
, or more properly plagioclase feldspar. Only limited solid solution occurs between K-feldspar and anorthite, and in the two other solid solutions, immiscibility occurs at temperatures common in the crust of the earth. Albite is considered both a plagioclase and alkali feldspar. In addition to albite, barium feldspars are also considered both alkali and plagioclase feldspars. Barium feldspars form as the result of the replacement of potassium feldspar.

The alkali feldspar

Alkali feldspar

orthoclase
Orthoclase

Orthoclase is an important Silicate minerals mineral which forms igneous rocks. The name is from the Greek language for "straight fracture," because its two cleavage planes are at right angles to each other....
(monoclinic), — KAlSi₃O₈
sanidine
Sanidine

Sanidine is the high temperature form of potassium feldspar 4O8. Sanidine most typically occurs in felsic volcanic rocks such as obsidian, rhyolite and trachyte....
(monoclinic) —(K,Na)AlSi₃O₈
microcline
Microcline

Microcline is an important igneous rocks-forming Silicate minerals mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium....
(triclinic) — KAlSi₃O₈
anorthoclase
Anorthoclase

The mineral anorthoclase is a crystalline solid solution in the alkali feldspar series, in which the sodium-aluminium silicate member exists in larger proportion....
(triclinic) — (Na,K)AlSi₃O₈

Sanidine is stable at the highest temperatures, and microcline at the lowest. Perthite

Perthite

Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar ....
is a typical texture in alkali feldspar, due to exsolution of contrasting alkali feldspar compositions during cooling of an intermediate composition. The perthitic textures in the alkali feldspars of many granite

Granite

Granite is a common and widely occurring type of Intrusion , felsic, igneous rock rock . Granite has a medium to coarse texture, occasionally with some individual crystals larger than the groundmass forming a rock known as Porphyry ....
s can be seen with the naked eye. Microperthitic textures in crystals are visible using a light microscope, whereas cryptoperthitic textures can only be seen using an electron microscope.

The plagioclase feldspars are triclinic. The plagioclase series follows (with percent anorthite in parentheses):

albite
Albite

Albite is a plagioclase feldspar mineral. It is the sodium Endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content....
(0 to 10) — NaAlSi₃O₈
oligoclase
Oligoclase

Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite and anorthite ....
(10 to 30) — (Na,Ca)(Al,Si)AlSi₂O₈
andesine
Andesine

Andesine is a feldspar mineral, a part of the plagioclase series.File:01722 Andesine.jpgIt is usually defined as having "%An" between 30 and 50....
(30 to 50) — NaAlSi₃O₈ — CaAl₂Si₂O₈
labradorite
Labradorite

Labradorite , a feldspar mineral, is an intermediate to calcic member of the plagioclase series. It is usually defined as having "%An" between 50 and 70....
(50 to 70) — (Ca,Na)Al(Al,Si)Si₂O₈
bytownite
Bytownite

Bytownite is a calcium rich member of the plagioclase solid solution series of feldspar minerals. It is usually defined as having "%Anorthite" between 70 and 90....
(70 to 90) — (NaSi,CaAl)AlSi₂O₈
anorthite
Anorthite

Anorthite is a compositional variety of plagioclase feldspar. Plagioclase is an abundant mineral in the Earth's Crust . The formula of pure anorthite is calciumAluminium2Silica2Oxygen8....
(90 to 100) — CaAl₂Si₂O₈

Intermediate compositions of plagioclase feldspar also may exsolve to two feldspars of contrasting composition during cooling, but diffusion is much slower than in alkali feldspar, and the resulting two-feldspar intergrowths typically are too fine-grained to be visible with optical microscopes. The immiscibility gaps in the plagioclase solid solution

Solid solution

A solid solution is a solid-phase solution of one or more soluble in a solvent. Such a mixture is considered a solution rather than a Chemical compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single wiktionary:Homogeneous phase ....
are complex compared to the gap in the alkali feldspars. The play of colors visible in some feldspar of labradorite composition is due to very fine-grained exsolution lamellae.

The barium feldspars are monoclinic and comprise the following:

celsian
Celsian

Celsian is an uncommon feldspar mineral, barium aluminosilicate, BaAl2Si2O8. The mineral occurs in contact metamorphic rocks with significant barium content....
— BaAlSi₃O₈
hyalophane
Hyalophane

Hyalophane or jaloallofane is a crystalline mineral with chemical formula [AlSi2O8] and a Mohs scale of mineral hardness of 6 ? 6?....
— (K,Na,Ba)(Al,Si)₄O₈

Feldspars can form clay

Clay

Clay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired....
minerals through chemical weathering.

Uses

Feldspar is a common raw material in the production of ceramic
Ceramic

File:Bridge from dental porcelain.jpgFile:Qing vase p1070256.jpgA ceramic is an inorganic, nonmetal solid prepared by the action of heat and subsequent cooling....
s and geopolymers.
Feldspars are used for thermoluminescence dating
Thermoluminescence dating

Thermoluminescence dating is the determination by means of measuring the accumulated radiation dose of the time elapsed since material containing crystalline minerals was either heated or exposed to sunlight ....
and optical dating
Optical dating

Optical dating is a method of determining how long ago minerals were last exposed to daylight. It is useful to geologists and archaeologists who want to know when such an event occurred....
in earth sciences and archaeology
Feldspar is one of several abrasive ingredients in Bon Ami
Bon Ami

Bon Ami, French language for "Good Friend", is a powdered household cleaner sold by the Faultless Starch/Bon Ami Company of Kansas City, Missouri, Missouri, United States....
, a brand of household cleaner in the USA.

In 2005, Italy was the top producer of feldspar with almost one-fifth world share followed by Turkey, China and Thailand, reports the International Monetary Fund

International Monetary Fund

The International Monetary Fund is an international organization that oversees the global financial system by following the macroeconomic policies of its member countries, in particular those with an impact on exchange rates and the balance of payments....
.

Feldspar

Etymology

Compositions

Uses

See also