Mineral of the Month – Ohio Flint August 2018 – Gitche Gumee Agate and History Museum

Ohio flint is the official gemstone of Ohio. It was designated the state stone in 1965. There are ridges and other deposits throughout Ohio, but most can be found in the eastern and central parts of the state.

Flint is a microcrystalline variety of silica (quartz). It is very closely related to Jasper and Chert since all three are made up of extremely small round crystals of silica. The microcrystals pack together so tightly (like BBs in a jar) causing these rocks to be opaque. Agate is a “first cousin” variety of microcrystalline silica, but its microcrystals are fibrous in shape and are translucent.

Flint, as well as chert and some jaspers, were highly prized by Native Americans since the rocks were able to be knapped to make arrowheads, spear points, beads, and other objects. Many Native Americans in the mid-West traveled to Ohio to collect flint. These tribes, as well as those living in Ohio, traded flint with other tribes in a wide geographic area.

The most famous deposit of Ohio flint is found in a six square mile ridge located in eastern Licking and western Muskingum counties. Flint from this ridge is called Vanport flint, which formed during the Pennsylvanian period between 286 and 325 million years ago. The actual deposit of flint ranges in thickness from one to twelve feet.