Crystal structures of near-end-member phlogopite at high temperatures and heat-treated Fe-rich phlogopite; the influence of the O,OH,F site

The crystal structure of end-member phlogopite-1M from White Well, Australia, was determined by refinement from single-crystal X-ray data, and cell parameters were refined at 20, 150 and 50 degrees C intervals to 600 degrees C; the rate of expansion of the cell dimensions was linear. The expansivity of c is 1.81 X 10 (super -5) / degrees C, with 1.40 and 1.34 X 10 (super -5) / degrees C for a and b, respectively. The OH-rich octahedra expand without changing shape significantly in contrast to F-rich octahedra in fluorophlogopite which become elongate approximately along the c axis. The interlayer site in phlogopite becomes elongate with increasing T relative to fluorophlogopite. The structure of an Fe-rich phlogopite-1M from Silver Crater, near Bancroft, Ontario, was refined at room-T and after heating at 904 degrees C for 24 hours; there was no change in Fe site occupancy from the octahedra to the tetrahedra.