Pargasiteferrotschermakite

Pargasiteferrotschermakite is a term used in mineralogy to describe amphibole compositions that lie in the solid solution between the endmembers pargasite and ferrotschermakite. It is not a formally recognized mineral species, but rather a descriptive designation for amphiboles whose chemical analyses show both sodium-rich, pargasite-like characteristics and iron-rich, ferrotschermakite-like characteristics. As such, it belongs to the calcic-sodic amphibole group within the broader amphibole supergroup and shares the characteristic double-chain silicate structure of amphiboles.

Chemically, pargasiteferrotschermakite covers a range of compositions with varying levels of Na, Ca, Mg, and Fe, with increasing Fe2+ content pushing the composition toward ferrotschermakite. Sodium and calcium contents can also vary, reflecting different metamorphic conditions such as pressure, temperature, and rock chemistry during crystallization. The term is used to indicate a continuum rather than a discrete endmember.

Occurrence and identification are typically summarised from electron microprobe analyses of amphibole-bearing rocks. When reported, the designation is used cautiously as a descriptive label for compositions intermediate between pargasite and ferrotschermakite, rather than as a separate mineral species. Some mineralogical databases and references may not list pargasiteferrotschermakite as a distinct entry, opting instead to report the material as a pargasite–ferrotschermakite solid solution or as a pargasite-rich ferrotschermakite.

In practice, the concept reflects the broader approach to amphibole chemistry, where many rocks yield minerals with continuous composition ranges rather than single, fixed endmembers.