Arkansas provides many great opportunities to explore nature, as the "Natural State" you will not want to forget your camera, a walking stick, and a buddy or two to go out and enjoy nature.
In this Earth Cache lesson you'll lean about another sedimentary deposit called Chert
After completing this Earth Cache you will have a better understanding of:
- The characteristics of Chert
- How Chert is formed
- Basic colors of Chert
- Old world uses
- Identification of Chert in the wild
Chert is a microcrystalline or cryptocrystalline sedimentary rock material composed of silicon dioxide (SiO2). It occurs as nodules, concretionary masses, and as layered deposits. Chert breaks with a conchoidal fracture, often producing very sharp edges. Early people took advantage of how chert breaks and used it to fashion cutting tools and weapons. The name "flint" is also used for this material.
Chert: This specimen of chert is about two inches (five centimeters) across. It displays conchoidal fracture and has broken to produce sharp edges.
How Does Chert Form?
Chert can form when micro-crystals of silicon dioxide grow within soft sediments that will become limestone or chalk. In these sediments, enormous numbers of silicon dioxide micro-crystals grow into irregularly shaped nodules or concretions when dissolved silica is transported to the formation site by the movement of groundwater. If the nodules or concretions are numerous, they can enlarge and merge with one another to form a nearly continuous layer of chert within the sediment mass. Chert formed in this manner is a chemical sedimentary rock.
Diatoms are microscopic, single-celled algae that live in marine or fresh water. They produce hard parts made of silicon dioxide.
Some of the silicon dioxide in chert is thought to have a biological origin. In some oceans and shallow seas, large numbers of diatoms and radiolarians live in the water. These organisms have a glassy silica skeleton. Some sponges also produce "spicules" that are composed of silica. When these organisms die, their silica skeletons fall to the bottom, dissolve, recrystallize, and might become part of a chert nodule or chert layer. Chert formed in this way could be considered a biological sedimentary rock.
What is Chert's Composition?
Chert is a microcrystalline silicon dioxide (SiO2). As chert nodules or concretions grow within a sediment mass, their growth can incorporate significant amounts of the surrounding sediment as inclusions. These inclusions can impart a distinctive color to the chert.
Marble Bar Chert: Outcrop of the 3.4 Ga Marble Bar Chert, Pilbara Craton, Australia. The hematite-rich chert has been used as evidence of high levels of atmospheric oxygen in the early Archean.
What Color is Chert?
Chert occurs in a wide variety of colors. Continuous color gradients exist between white and black or between cream and brown. Green, yellow, and red cherts are also common. The darker colors can result from inclusions of sediment or organic matter. The name "flint" is often used in reference to the darker colors of chert. Red to reddish brown cherts receive their color from included iron oxide. The name "jasper" is frequently used for these reddish cherts.
What are the Uses of Chert?
Chert has very few uses today; however, it was a very important tool-making material in the past. Chert has two properties that made it especially useful: 1) it breaks with a conchoidal fracture to form very sharp edges, and, 2) it is very hard (7 on the Mohs Scale). The edges of broken chert are sharp and tend to retain their sharpness because chert is a very hard and very durable rock. Thousands of years ago people discovered these properties of chert and learned how to intentionally break it to produce cutting tools such as knife blades, arrowheads, scrapers, and ax heads. Tons of chert fragments have been found at locations where these objects were produced in what was one of the earliest manufacturing activities of people.
Chert Arrowhead: A chert (flint) arrowhead bound to a wooden arrow shaft with sinew. Flintlock:A close-up of the lock of a flintlock rifle, a weapon of the 18th century used in the Revolutionary War. Note the piece of chert (flint) in the hammer.
Chert is a very hard material that produces a spark when it is struck against steel. The heat from this spark can be used to start fires. A "flintlock" is an early firearm in which a charge of gunpowder is ignited by a flint hammer striking a metal plate. A variety of metamorphosed chert known as "novaculite" has a porous, even texture that makes it useful as a sharpening stone. The Arkansas Novaculite Formation has become world famous as a source of high-quality sharpening stones and novaculite abrasive products.
Did you Know?
Chert is not found everywhere. It was a precious commodity that early people traded and transported long distances. As early as 8000 BC, the people of what are now England and France dug shafts up to 300 feet deep into layers of soft chalk to mine chert nodules. These are some of the oldest mining operations ever discovered.
Requirements: (please do not put your answers in the log)
Now that we learned the basic qualities of Chert, take a moment to study ground zero. With the information above, and information at GZ you should be able to answer the following questions. You have 24 hours to send me an email (found in my geocaching profile) with the correct answers. Failure to do so will result in the removal of your "Found it log". Please add the GC code and title in the subject line. If you are sending answers for multiple people in your group, please add all the names in your email to ensure they don't have their log deleted :) Photos with you/group of the area would be greatly appreciated.
1 In your own words explain what Chert is.
2 With the information provided at Ground Zero there is a block of Boone Limestone above what type of Formation?
3 How old is the Chert Estimated to be at Ground Zero.
4 According to the information provided and observing with your own eyes, what color is the Chert at Ground Zero?Estimated
5 What is another Term for Chert?
6 What State is famous as a source of high-quality sharpening stones and novaculite abrasive products?