A Fe-rich dioctahedral mica with tetrahedral Al (or Fe3+) usually greater than 0. 2 atoms per formula unit and octahedral R3+ correspondingly greater than 1. 2 atoms. A generalized formula is K(R1. 333+R0. 672+)(Si3. 67Al0. 33)O10(OH)2 with Fe3+>>Al and Mg>Fe(II) (unless altered). Further characteristics are d(060) >0. 151 nm and (usually) broader infrared spectra than celadonite. Mixtures containing an iron-rich mica as a major component can be called glauconitic.