Magnesian Tourmaline from Renfrew, Ontario

The specimens of the mineral examined were obtained from a limestone quarry near the town of Renfrew. The tourmaline occurs near the contact of grey granite-gneiss and crystalline limestone of the Grenville series. The gneiss is intrusive into the limestone, and contact effects are observable both in the intrusive and in the intruded rock. The gneiss consists of quartz, plagioclase, micrccline, and a green pyroxene. The limestone is composed (almost entirely) of calcite, but contains some graphite. The secondary minerals occurring in both limestone and gneiss are, besides the tourmaline, pyrrhotite, titanite, and muscovite.