Slate deposits of Maine

The slates of Maine lie in the center of the state within the southern Piscataquis County, south to south-east of Moosehead Lake and east to west of the Seebac Lake in the vicinity of the villages Monson, Blanchard and Brownville.

The slates were mined within the Lower Devonian 'Carrabesset Formation' which was deformed during the Acadian mountain building. The thickness of the minable zone is between 98 - 197 ft. whereas the the best slates steam from an about 8,2 ft. thick slate bed (Caldwell, 1998).

According to Dale et al., the colour of the slates at Nort Blanchard varies between bluish-grey, grey to black which partly show a purple or brownish shade. Within the single slate deposits the smoothness and the shine is varying. The well developed fracture cleavage is sometimes crossed by a crenulation foliation. Dale (1914) mentioned the following mineral proportions, in order to their amount: muscovite, quartz, chloride, magnetite, biotite, pyrite, graphite, carbonate and turmaline. The slates were used for roofing and the electricity industry. At the moment no slate quarry seems to be active in Maine.