A trioctahedral member of the true mica group with an approximate chemical composition of (NH4, K)(Fe1.33Mg0.71Al0.42Ti0.22)Si2.67Al1.33O10(OH)2. The characterizing feature is the NH4 (NH4 > K) in the interlayer site and the trioctahedral sheet; the composition suggests that suhailite may be described as an ammonium-rich biotite. Difficulties in separating suhailite from impurity phases, stacking disorder and a high numbers of defects prevented structural characterization. Impurity phases and volatility of NH4 limited the accuracy of the chemical analysis. Suhailite occurs in gneisses from the Betic Cordillera, Spain, and formed from primary annite during the annite to fibrolite transformation, probably at temperatures up to ~500 oC (Ruiz Cruz et al., 2009).
Cf., tobelite