Phyllite
in mineralogy, a mineral found in small shining scales sca or plates in a clay-slate. Essentially a hydrated markable stinging power, and are probsilicate of alumina, sesquioxide and protoxide of iron, protoxide of manganese, and potash. Found in Massachusetts and Rhode Island. Also a name given to some slaty rocks of cryptocrystalline to microcrystalline texture, apparently intermediate between mica-schist and ordinary clay slate.