Meramec Station Road Calcite

Finding calcite in Limestone Cliffs near St. Louis

- ROBERT BEARD

Meramec Station Road, located on the outskirts of southwestern St. Louis, Missouri, has a section of limestone cliffs that offer an opportunity to collect calcite. The cliffs are well exposed along the southern side of Meramec Station Road. Parking is adequate for several vehicles, and the area is frequently visited by local rockhounds and people who just want rocks for their garden. The area is best described as commercial and residential. Collecting is along the base of the cliffs, and there are large talus piles along the length of the cliffs. The calcite occurs in small veins in the limestone. Masses of white calcite with prominent cleavage can be found in the talus and range in size from an inch to nearly a foot. Some of the calcites also have voids that have white to clear dogtooth calcite crystals.

CALCITE BACKGROUND

Calcite is calcium carbonate, or CaCO3. It is an important rock-forming mineral and is found in a wide variety of geologic environments. Calcium carbonate occurs as both a primary mineral, which formed at the same time as the host rock, and as a secondary mineral, which formed later than the host rock. Calcite is 3 on the Mohs hardness scale, and it is easily scratched by steel and most other rocks.

While it has a simple chemical formula, calcium carbonate has a wide variety of crystal habits, and its identification is further complicated by the fact that calcium carbonate has three polymorphs. These are calcite, aragonite and vaterite.

Calcite is commonly found in many rocks, and it is the most stable form of calcium carbonate. It is often found in veins in fractured rocks and is also common as a primary mineral in sedimentary rocks such as limestone and dolomite. Since it is the most stable form, it is the most common of the polymorphs.