Dolomite is a sedimentary rock rich in the common rock-forming mineral that bears the same name. Though it is typically harder and heavier than limestone, dolomite is sometimes considered a variety of that type of rock.

The Potosi Dolomite gains its moniker from Potosi, Missouri, where the large formation of cherty carbonate rocks was first identified in the 1800s. From exposures at its type locality, geologists traced the rock mass beneath the surface of the Earth to exposures of the material found in northern Illinois. In that locale, the Potosi Dolomite is sometimes alternatively referred to as the Trempealeau Formation. The term Potosi Dolomite is also frequently utilized in regard rocks found in Indiana.

Customarily considered among the youngest rocks in the Cambrian System, the Potosi Dolomite is chiefly comprised of fine- to medium-grained dolomite. The rocks also contain some slender interbeds of shale or siltstone, as well as intermittent grains of sand, which are most prevalent in the northern parts of Indiana. In some areas, erratic inclusions of chert and glauconite also occur in the Potosi. The color of the rocks ranges from light gray and brown to much darker shades of the same colors.

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