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An endmember (also end-member or end member) in
mineralogy Mineralogy is a subject of geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is com ...

mineralogy
is a
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

mineral
that is at the extreme end of a mineral series in terms of purity of its chemical composition. Minerals often can be described as
solid solution A solid solution describes a family of materials which have a range of compositions (e.g. AxB1−x) and a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word "solution" is used to desc ...

solid solution
s with varying compositions of some
chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elements cannot be broken down into simp ...
s, rather than as substances with an exact chemical formula. There may be two or more endmembers in a group or series of minerals. For example,
forsterite Forsterite (Mg2SiO4; commonly abbreviated as Fo; also known as white olivine) is the magnesium-rich end-member of the olivine solid solution series. It is isomorphous with the iron-rich end-member, fayalite. Forsterite crystallizes in the orth ...

forsterite
() and
fayalite Fayalite (Fe2SiO4; commonly abbreviated to Fa) is the iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and gro ...

fayalite
() are the two end-members of the
olivine The mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. R ...

olivine
solid-solution
solid-solution
series, varying in and in their chemical composition. So, the chemical formula of olivine can be better expressed as or . As another example, the
tectosilicate Silicate minerals are rock-forming mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs na ...
feldspar Feldspars are a group of rock-forming aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity ...
can be described as a solid solution of the endmembers
K-feldspar
K-feldspar
AlSi3O8
albite Albite is a . It is the sodium of the plagioclase series. It represents a plagioclase with less than 10% content. The pure albite endmember has the formula 38. It is a . Its color is usually pure white, hence its name from ''albus''. It is ...

albite
aAlSi3O8and
anorthite Anorthite is the calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physic ...
aAl2Si2O8What is Feldspar?
Industrial Minerals Association. Retrieved on February 9, 2008.
A specific feldspar can have varying quantities of
potassium Potassium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

potassium
 (K),
sodium Sodium is a with the  Na (from Latin ''natrium'') and  11. It is a soft, silvery-white, highly reactive . Sodium is an , being in of the periodic table. Its only stable is 23Na. The free metal does not occur in nature, and must be ...

sodium
 (Na) and
calcium Calcium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

calcium
 (Ca).


See also

*
Larvikite Larvikite is an igneous rock, specifically a variety of monzonite, notable for the presence of thumbnail-sized crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arra ...

Larvikite


References

{{mineral-stub Mineralogy