Non-Mineral Resources of the Exotic Terrane

Figure 7.12: Principal non-mineral resource-producing localities of the Exotic Terrane. Figure adapted from 1998 United States Geological Survey State Mineral Information.

The Exotic Terrane region has a variety of non-mineral resources, many similar to those of the Appalachian/Piedmont region because of the rock types these regions share. Coal is even found in the Exotic Terrane region in the Narragansett and Boston basins, though it is not currently mined (Figure 7.12).

Sedimentary Rock

The sedimentary rock non-mineral resources of the Exotic Terrane are similar to those of the Appalachian/Piedmont and Inland Basin regions. Brownstone is quarried from the rift basin in the Connecticut River Valley; clay and shale are mined from glacial deposits and marine shales of the Silurian and Devonian; and cement and crushed rock are produced from a variety of rock types to be used in the construction industry.

Igneous Rock

Granites, formed from intrusions of magma during the Taconic and Acadian mountain-building events, appear all over the Exotic Terrane region. It is quarried throughout the region for use in buildings and monuments, though the demand is not as great as it was in the past. Granite is more expensive to quarry than the much softer marbles found in Vermont, and the issue of transportation raises costs even higher. Though New Hampshire is known as the Granite State for its abundance of granite of varying ages, Barre, Vermont is known as the granite center of the world. The famous Barre Granite, formed from an intrusion of magma into overlying rock during the Acadian mountain-building event, is a uniform light gray that takes an excellent polish and is widely used for monuments.

Metamorphic Rock

Quartzite is being actively quarried from Silurian and Devonian metamorphic rock in Connecticut. Quartz is derived from sandstone deposited in the Iapetus Ocean. The sandstone became compressed, metamorphosed and attached to the continent when Baltica collided with North America. When sandstone is metamorphosed, it recrystallizes to become quartzite.

Fossil Fuels

Coal is found in the Narragansett Basin of Rhode Island and Massachusetts. The coal was formed during the Pennsylvanian when the collision of North America and Baltica compressed the Avalonia microcontinent caught in the middle. The collision buckled the crust to form small basins that gradually filled in with sediment. Accumulations of dead plant material in the swampy basins provided the proper conditions for minor amounts of bituminous coal to form, though there are not large enough amounts to make mining profitable.