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Rhode Island Rocks and Minerals
Rhode Island is one of the worst states for finding gem grade rocks and minerals.
Once a plain not much above sea level, Rhode Island has been uplifted and its surface covered by stream action into low hills and valleys, and some of the latter have become ocean bays. Glaciation completed the work of forming the surface. A large terminal moraine was formed in the ocean at the edge of the ice sheet during the first pulse of glaciation, creating Block Island, Long Island, Martha's Vineyard and Nantucket. Rhode Island was glaciated twice leaving much of its surface rocks and soils, but ice was gone about 14,000 years ago, shortly before the initial migration of humans to North America. Some locations in northeastern Rhode Island and in the East Greenwich Group are granite and volcanic igneous rocks. Sedimentary rocks are common in the Narragansett Basin in the eastern part of the state.
Rhode Island is most known for granite and coal mining as well as sone gold mining and current extraction of aggregates for road and building construction. Rhode Island has several gold mines, some of which were mined commercially off and on for many years, but the mines were never really successful due to the low-grade deposits and sporadic nature of the gold deposit.
Westerly granite, found between Westerly and Bradford is a pink to gray fine-grained granite composed of glassy quartz, black mica and feldspar. Westerly granite was extensively quarried between 1845 and 1955 and used in construction in many historic areas.
In 1809 the General Assembly announced a $10,000 lottery to develop a coal mine in the Narragansett Basin in Portsmouth. One million tons of coal were ultimately extracted from the mine. Mid-size coal mines also operated in Cranston and Pawtucket through the 1930s.
Rhode Island officially designated Bowenite Serpentine as its state mineral in 1966. Found in Northern Bowenite Serpentine is a pretty waxy green rock. It was first found in the Dexter Quarry in Lincoln, Providence Co., Rhode Island.
Rhode Island also officially declared Cumberlandite its state rock in 1966. Cumberlandite is an uncommon mafic igneous rock scattered throughout the Narragansett Bay watershed as far as Martha's Vineyard, it is also found in Sweden.
You can find some agates, jaspers, and carnelians on the state’s beaches. And the gravel beds of the Moosup River contain a variety of minerals including epidote, pyrite, garnet, and labradorite.
Before venturing out-do some research on where and what you can collect. Remember you must have permission to collect on private property.
See my page on Rockhounding Rules for general information on the rules of collecting rocks on various lands.