albitedominated

Albitedominated is a petrographic descriptor used to characterize rocks and sediments in which albite, the sodium endmember of plagioclase (NaAlSi3O8), is the most abundant feldspar. The term emphasizes the endmember composition of the plagioclase feldspar assemblage rather than the overall mineral content.

Geological settings: Albite-dominated assemblages occur in certain igneous rocks such as Na-rich granitoids and plagioclase-rich lithologies where calcium-rich endmembers are scarce. In metamorphic systems, albite-rich textures can form during albitization or under Na-rich fluid regimes. In sedimentary rocks, albite can predominate in feldspar-rich sandstones derived from source areas with abundant albite-bearing rocks.

Identification and features: Determination relies on modal analysis from petrography, X-ray diffraction, or electron microprobe data, with albite constituting the majority of the feldspar phase. Albite-twinning and pale coloration help distinguish albite from orthoclase. Alteration processes (albitization) can modify surrounding minerals and affect interpretation.

Significance and caveats: The label aids in describing source characteristics and magmatic differentiation. It should be used with caution, as alteration and weathering can overprint mineralogy, and the boundary between albite-dominated and generally feldspar-rich rocks may be gradual.