end-member

Noun

endmember (plural endmembers)

1. A member at one end of a range or series made up of similar members.
   • Most significant is the observation that the vaporous for the more volatile end member occupies a decreasingly smaller portion of the diagram as the other end member becomes less volatile. Ultimately, when the less volatile end member is essentially involatile, the vaporous of the volatile end...1970, Arnold Reisman, “Condensed-vapor Phase Binary Diagrams Continued—Incongruently Vaporizing Systems”, in Phase Equilibria: Basic Principles, Applications, Experimental Techniques (Physical...
2. (specifically) A mineral that occurs at one end in a range of solid solutions.
   • This group of tetragonal silicates seems to form a graduated series from akermanite to gehlenite, the constitution of the two end[-]members being (where R = Ca, with less Mg, Mn, Fe, Na₂): / Akermanite, R₄Si₂O₁₀, or R₃(RSi)Si₂O₁₀, / Gehlenite, R₃Al₂Si₃O₁₀, or R₃(Al₃)Si₃O₁₀, […]1892, The Mineralogical Magazine and Journal of the Mineralogical Society, volume 10, London: H[umphrey Sumner] Milford, Oxford University Press, →OCLC, page 33