Orientation of the dipole moments of hydroxyl groups in oxidized and unoxidized biotite.

Observations of the infrared absorption bands attributed to the stretching vibrations of hydroxyl groups in biotite containing predominantly ferrous iron show that the dipole moments of the hydroxyls associated with ferrous iron are oriented perpendicular to the cleavage plane of the lattice. Oxidation in the biotite from ferrous iron to ferric iron results in the disappearance of the infrared absorption bands due to the hydroxyls associated with ferrous iron. The dipole moments of the hydroxyls associated with ferric iron in the oxidized biotite have been shown to be in an inclined position with respect to the cleavage plae. Our experiments confirm the hypothesis of Barshad and Kishk regarding the effect of oxidation on the replaceability of interlayer potassium ions in biotite by ammonium ions.