Ohio State Gemstone
Flint is a variety of chert, which in turn is a sedimentary form of quartz with microscopic crystals. Since it is composed largely of quartz but also has small amounts of other minerals, flint is technically a rock. It occurs in dark gray, black, green, white, or brown masses. Specimens with iron impurities have a red tint. The most common type of Ohio flint is white with light gray streaks, while the most prized are the colored types.
Flint mined from Flint Ridge, a vein in Ohio almost 8 miles (12.87 km) long, is called Ohio flint. In 1888, American historian Henry Howe noted, "This 'Flint Ridge' must have been as valuable to the Indians ... as the coal and iron mines of Ohio and Pennsylvania are to the white men of the present day." This area in Ohio’s Appalachian foothills has been called "The Great Indian Quarry of Ohio." Flint Ridge State Memorial is on the list of National Historic Places. The site offers a museum that was built around a restored prehistoric quarry pit. The Ohio legislature adopted Ohio flint as the official state gem in 1965.
FORMATION AND OCCURRENCE
Flint is the variety of chert that occurs as masses in sedimentary rocks such as limestone and chalk. It is formed by chemical changes in compressed sedimentary rock. One theory says that the silica needed to form flint comes from sponges that lived in prehistoric seas. Fossilized marine vegetation has been found in some flint specimens. Ohio flint was deposited 438 to 286 million years ago in shallow, tropical seas that covered what is now Ohio.
GEOGRAPHIC DISTRIBUTION OF LARGEST FLINT SOURCES
Because flint splits into thin, sharp splinters or blades, this rock was used in the Stone Age to make flint spear points, arrowheads, knives, and other tools and weapons. Flint has reportedly been mined since the Paleolithic age, the prehistoric period known for the development of the first stone tools. Flint was used as a trading item in ancient times, and was favored by the Hopewell Culture (100 BCE–500 CE) for its usefulness and beauty. Flint artifacts from Flint Ridge have been discovered as far away as the Gulf of Mexico and the Rocky Mountains.
Flint has been used from ancient Roman times to the present as a building material, often combined with stone or brick. It was quite common in the early Middle Ages in parts of southern England where other local building stone was not available.
When a flint edge is struck against steel, it produces a spark. This property was utilized in fire-starting tools and firearms by early European settlers and is still used today in some rifles. Early European settlers also used flint to sharpen tools and grind grain. Flint pebbles are used today in mills to grind flour, ceramics, glazes, and other materials.
Since Ohio flint is found in many colors and its surface will take a high polish, it is used in jewelry. Ohio's state gemstone is most often found in pendants.
Group: Often classed in Quartz Group (a subgroup of Tectosilicates) although it is a rock
Chemical Formula: C20H19F3N2O4
Crystal Structure: Hexagonal
Hardness (Mohs): 7
Color: Has been found in almost every color
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press