quartzfeldspardominated

Quartzfeldspar is a descriptive term used in geology to refer to rocks in which quartz and feldspar are the dominant minerals. It is not the name of a mineral, but a petrological descriptor applied to many felsic igneous rocks and their metamorphic equivalents.

In these rocks, quartz (SiO2) typically accounts for a substantial portion of the mineralogy, while feldspars (both alkali feldspars such as orthoclase and microcline, and plagioclase members) form the other major component. The exact proportions vary; typical granitic rocks contain roughly 20–60% quartz and 40–70% feldspars by volume, with accessory minerals such as mica, hornblende, and zircon.

Textures such as graphic granite, where quartz and alkali feldspar intergrow in a distinctive mosaic, are well-known examples of quartzfeldspar textures. In some rocks, feldspars and quartz achieve interlocking crystal frameworks that give a coarse, granular appearance.

Occurrence and formation: Quartzfeldspar rocks form by partial melting and crystallization of silica-rich magmas in the continental crust. They occur as intrusive bodies such as granite and granodiorite and, in altered or metamorphic contexts, as quartzofeldspathic metasedimentary or meta-igneous rocks (gneiss, schist) where the mineralogy remains quartz- and feldspar-dominated.

Significance: The quartz–feldspar assemblage is a defining characteristic of felsic crustal rocks and contributes to their physical properties, including color, density, and strength. The term helps classify rocks in petrology and is used in studies of crustal composition and tectonics.