Basalt fibers- The basalts are extrusive naturally mined igneous rock. They are dense fine-grained rocks that are of very dark color- green or black and form when molten lava from deep in the earth's crust rises up and solidifies. Slightly coarser old sheets of basalt, now partially altered but still dark in color, are extensively quarried, crushed, and sold as "traprock". Basalt is a hard, dense, dark volcanic rock composed chiefly of plagioclase, pyroxene, and olivine, and often having a glassy appearance. The cut fibers are coated with a sizing treatment, which makes them highly compatible with epoxy and phenolic resins.