Connecticut’s geology includes igneous, sedimentary, and metamorphic rock, as well as minerals and ore. As of the date of publication, most the mining operations and quarries have been shut down in Connecticut because of the high cost of operation. However, as of the early 2000s, there were still quarries in operation, including one dolomite quarry, four limestone quarries, five granite quarries and nine basalt quarries.
Lava or other molten material in the earth’s crust forms igneous rock. Granite, an igneous rock, is found in the eastern part of the state. Basalt, another igneous rock, often called “traprock,” is found in the hills of central Connecticut’s lowlands. Basalt used to be mined in quarries in central Connecticut, and was used to build roads, but those quarries have closed.
Rock particles under water become cemented together under pressure and over time to form sedimentary rock. Limestone, a sedimentary rock found in Connecticut, is present primarily in the state’s western edges and northwest corner. Shale and red sandstone, other sedimentary rocks, are in the state’s central lowlands.
Igneous or sedimentary rock, when made denser by exposure to intense pressure, form metamorphic rock. Metamorphic rock makes up most of the rock in the state. Common types of metamorphic rock include slate and marble. For a period, marble quarries opened in Connecticut. However, the quarries have since been shut down.
Minerals & Ore
Minerals are not especially plentiful in Connecticut relative to other geographic areas. Clay is a mineral found in Connecticut’s central valley; it was mined for brick making. Ore, rock that contains deposits of a metal, is likewise not especially plentiful in Connecticut. Though Connecticut had copper and iron mining in the past, the mining operations have since become too expensive for the amount of metal that could be mined, and were shut down.