chert - teaching hand specimen of light tan chert
This chert is too soft for flint knapping, though a typical chert. It is very similar to glass in hardness, so will not easily scratch a glass plate. However, when tested against the rear window of a VW van, it left a nice scratch in that glass.
This particular chert is tan or banded tan and brown and is from a deposit associated with magnesite, magnesium carbonate, a common association. Chert is a cryptocrystalline variety of quartz that will break with very sharp edges. For this reason it was sought after by stone-age tool makers. Flint is the related form that is found in chalk beds.
Some of these specimens were sharp-edged when collected. Any sharp edges have been rubbed against a geologist's hammer to remove the "edge," though the specimens appear untouched. This is a very typical chert.
If you are a science or earth science teacher purchasing this as a teaching specimen for your class, this should be compared with other varieties of quartz: agate, jasper, chalcedony and tiger eye, which are all microcrystalline or cryptocrystalline - showing no crystal structure.
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