Endmember (mineralogy)
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An endmember in mineralogy is a mineral that is at the extreme end of a mineral series. For example the plagioclase series of tectosilicate minerals within the feldspar family ranges from albite to anorthite (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium and calcium atoms can substitute for each other in the mineral's crystal lattice structure. Thus, both albite and anorthite are endmembers of the plagioclase series. Albite is also the endmember of the alkali or K-feldspars whose series ranges from pure NaAlSi3O8 to pure KAlSi3O8.
