Phyllite is between slate and schist on the metamorphic scale. The platy minerals such as mica, but not yet large enough to be clearly identified. Phyllite looks a lot like slate, but its glossy sheen gives it away.

Phyllite usually has cleavage and is composed mainly of very fine crystals of either muscovite or chlorite.

Information provided by Patrick M. Colgan, Northeastern University
http://www.casdn.neu.edu