Dark coloured micas are strongly pleochroic. Accurate determinations of the optical orientation, as well as the symmetry of the etching figures on the cleavage planes, seem to suggest that the micas, except muscovite, may be anorthic rather than monoclinic in crystallization.
anorthic הגייה עם משמעויות, מילים נרדפות, הפכים, תרגומים, משפטים ועוד