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. Mineralogy is an earth science that involves the chemistry, crystal structure, and physical (including optical) properties of minerals. ... Minerals are natural compounds formed through geological processes. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... The silicate minerals make up the largest and most important class of rock-forming minerals. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... Albite is an alkali feldspar mineral. ... Anorthite is one of the plagioclase feldspars, an important group of minerals abundant in the Earths crust. ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Atomic mass 22. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ... Properties For alternative meanings see atom (disambiguation). ... Crystallography (from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write) is the experimental science of determining the arrangement of atoms in solids. ...