pargasiterich

Pargasiterich is a descriptive term used in mineralogical and petrological contexts to describe rocks or mineral assemblages that contain a relatively large proportion of pargasite, an alkali amphibole. It is not a formal mineral species, but a qualitative descriptor that signals a dominance or conspicuous presence of pargasite within the rock.

Pargasite itself is an alkali amphibole in the hornblende group, typically rich in sodium and calcium and containing magnesium and iron. It forms under conditions where Na and Ca are available in the system, commonly in metamorphic environments and in some alkaline igneous rocks. Pargasite-bearing assemblages are often encountered in high-temperature, medium- to high-pressure metamorphic terranes and can occur in contact metamorphic zones as fluids alter existing mineralogy.

In rocks described as pargasiterich, pargasite can define the amphibole portion of the mineralogy and influence texture and weathering behavior. Identification relies on petrographic observation, chemical analysis (for Na-rich amphiboles), and mineralogical techniques such as electron microprobe analysis or X-ray diffraction to confirm the amphibole subtype and differentiate it from other hornblende varieties.

Significance of pargasiterich rocks lies in the insights they provide into fluid composition and metamorphic history. The dominance of pargasite indicates sodium- and calcium-rich conditions and can help constrain pressure–temperature paths and metasomatic processes during rock evolution. Because the term is descriptive, it is most informative when accompanied by quantitative modal data.

See also: pargasite, hornblende group amphiboles, metamorphic petrology, metasomatism.