pegmatite. Photo by Henry Berry and the Maine Geological Survey
Granitic pegmatite is a coarse-grained rock with a similar composition to granite. Many of Maine’s unique and highly sought after gems and minerals are found in granitic pegmatite, including the state mineral tourmaline. Quartz, feldspar, and mica have been commercially mined from granitic pegmatite in the state.
Pegmatite is an intrusive igneous rock which means that it is formed when magma penetrates existing rock and solidifies. The large crystals that are characteristic of pegmatite are formed because the magma contains a large amount of dissolved fluid, usually water, that allows the crystal-building ions to move freely and rapidly form crystals. Maine has several world-class locations for mineral and gem hunting thanks to our many occurrences of granitic pegmatite.