Ferrimuscovite and celadonite substitutions in muscovite from Fe3+-rich low-grade psammitic rocks (Northern Apennines,Italy)

Electron microprobe and wet-chemical data of muscovites from pyrophyllite- or K-feldspar-bearing Fe3+-rich rocks of the Verrucano metasediments are reported. A close relationship has been found between muscovite composition and bulk-rock chemistry. The extent of celadonite and ferrimuscovite substitutions increases progressively from pyrophyllite- to K-feldspar-bearing samples. The mutual cation substitutions reveal: (1) an almost ideal Tschermak substitution; (2) a close positive correlation between the (Mg + Fe2+) and Fe3+ contents; and (3) a negative correlation between the octahedral and interlayer occupancies. The extent of celadonite and ferrimuscovite substitutions of muscovite from magnetite-bearing rocks has been constrained at moderate pressure in low-temperature metamorphism. © 1989.