Pikes Peak Pebble Pups

Pikes Peak Pebble Pups

Tuesday, July 2, 2013

The Flint Ridge Formation

By Luke Sattler, Colorado Springs Mineralogical Society

Near the town of Hopewell, Ohio is the extraordinary geological feature known as Flint Ridge, a deposit of flint that is about three miles wide and nine miles long and trends from east to west. The Flint Ridge Formation ranges between two and 10 feet thick. Flint Ridge Flint is prized among flint knappers—both in the  distant past and the present—for its rich and vibrant colors and how easily it knaps.

Historic marker about Flint Ridge

Around 10,000 years ago, Native Americans mined the flint for stone tools. Native American tribes that were thought to be in the area around 10,000 years ago were the Adena and the Hopewell. These two tribes likely mined in the Flint Ridge area. The flint location was so valuable that the formation was considered a neutral zone—a place of peace, where the two different tribes would put their weapons aside and could gather flint without the constant threat of violence. The pits—where they mined flint for the purpose of knapping—are still visible today. 

Flint Ridge Flint showing its range of colors

Flint is formed from dissolved, silica-rich particles of ancient sponges and plankton that died and fell to the bottom of the sea. When this material accumulated it formed a silica gel and filled cavities found naturally on the sea floor. While in these cavities, this silica-rich gel hardened into a mass eventually forming flint. Sometimes the flint will form around the shells of other organisms; when this happens the fossil will be inside or encased by the flint.

Fossil organisms like this one form the silica gel that eventually forms the flint.
This is a scanning electron microscope image.
 Note measurement bar of 1 micron in the left corner.

 Flint Ridge Flint, like many other different kinds of flint, needs to be heat treated or cooked to be easily knapped. Heat causes the molecules in the flint to expand and become more brittle—making it easier to flake. The Native Americans would heat the flint by burying it under their fire pits and build fires on top of the buried flint. While the fire burns the flint cooks, making it brittle and easier to knap. Today knappers also use fire pits. Modern knappers may also use kilns or turkey roasters that are more cost effective than a kiln. Both still do the same job but are faster and better controlled than a fire.

Flint Ridge Flint comes in a variety of colors, ranging from vibrant blues to teal, red, turquoise, peach, tan and grey. Different minerals in the surrounding rock cause the flint to form different colors. For instance, iron-rich minerals cause red colors while copper creates blue and teal colors. Flint Ridge Flint is also prized for its beauty as cutting material in the lapidary world. Some Flint Ridge Flint contains small cavities of quartz crystals, which make an attractive display on a knapped point or a cabochon.

Here are some examples of Flint Ridge Flint knapped by great knappers from around the country.

Flint Ridge Corner Tang Knife. Knapped by James Shipley.
James lives near Casper WY. He has been knapping for 15 years.

Flint Ridge Point. Knapped by Ed Mosher.
Ed lives in Monticello IN. he has been knapping for 23 years

Welcome! This is the gateway to adventure and discovery

Through this blog pebble pups and junior members of the Colorado Springs Mineralogical Society can access their lessons, work on assignments and projects, and receive details about field trips in the Pikes Peak Region. This Internet program is also suitable for young people who are interested in Earth science but do not live near a rock club or gem and mineral society or for young people anywhere who want a deeper dive into these topics. The only requirement is that all participants must be members of the Colorado Springs Mineralogical Society and must fill out the CSMS membership form (under important websites) and send their registration and membership fee in. Steven Veatch is the senior instructor and will need an email from you with your name, address, phone number, and permission from your parents to participate in this program.