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Black jasper rock12/5/2023 ![]() ![]() 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. It was a precious commodity that early people traded and transported long distances. 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.Ĭhert is not found everywhere. ![]() 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. The edges of broken chert are sharp and tend to retain their sharpness because chert is a very hard and very durable rock. 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). Chert Used to Make Sharp ToolsĬhert has very few uses today however, it was a very important tool-making material in the past. Image copyright iStockphoto / Brian Brockman.Ĭhert cabochons: Occasionally, specimens of chert with attractive colors or interesting patterns are cut as gemstones. Chert formed in this way could be considered a biological sedimentary rock.Ĭhert Arrowhead: A chert (flint) arrowhead bound to a wooden arrow shaft with sinew. In some areas the sedimentation rate of these materials is high enough to produce rock layers that are thick and laterally extensive. When these organisms die, their silica skeletons fall to the bottom, dissolve, recrystallize, and might become part of a chert nodule. Some sponges also produce "spicules" that are composed of silica. These organisms have a glassy silica skeleton. In some parts of the ocean and in shallow seas, large numbers of diatoms and radiolarians live in the water. Some of the silicon dioxide in chert is thought to have a biological origin. They produce hard parts made of silicon dioxide. Chert formed in this manner is a chemical sedimentary rock.ĭiatoms are microscopic, single-celled algae that live in marine or fresh water. ![]() If the nodules or concretions are numerous, they can grow large enough to merge with one another to form a nearly continuous layer of chert within the sediment mass. In these sediments, enormous numbers of silicon dioxide microcrystals grow into irregularly-shaped nodules or concretions when dissolved silica is transported to the formation site by the movement of groundwater. Chert can form when microcrystals of silicon dioxide grow within soft sediments that will become limestone or chalk. ![]()
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