Zonally grown mica from a granitic pegmatite, Myo-ohage, Makino-cho, Shiga Prefecture, Japan.

Abstract

A zonally grown mica from a granitic pegmatite was examined with the following results.
(1) The mica may be a chemically discontinuous overgrowth of iron-muscovite (marginal part) on biotite (core).
(2) They are crystallographically continuous and both are of 3-layer monoclinic polytype.
(3) X-ray precession photographs of the mica show that the mica is a twin crystal, the twinning plane of which is (07^-1).
(4) The diffuseness of the X-ray reflection spots of the mica indicates that the crystal lattice is regular in the direction approximately parallel with the a-axis while it is less regular in the direction approximately parallel with the b- and c-axes.