I’m a little confused about chert and flint. In your gemstone listing entry on quartz, you identify both chert and flint as examples of cryptocrystalline quartz. They are described together as “opaque, dull gray, or whitish chalcedony, very compact and hard.” Are chert and flint the same mineral?
Flint Is A Variety of Chert
Although there is a lot of confusion on this, chert refers to cryptocrystalline or polycrystalline quartz that usually forms as nodules in limestone. Flint is reserved for such material that forms in chalk or marl. Flint is simply a type of chert. (At least this was the distinction that was made in the literature when I was a geology student 35+ years ago).
Mozarkite: The Show Me Chert
There’s more to the story regarding chert and flint. Although chert and flint are described as “opaque, dull gray, or white” and said to rarely appear as jewelry, this is not always the case.
I am a member of the St. Louis Mineral and Gem Society. Our club petitioned the state of Missouri to adopt a state rock in 1967. The name of the Missouri state rock is mozarkite, a type of chert that is found in the area of Lincoln, Missouri. Mozarkite contains a multitude of colorful swirls and patterns, such as red, blue, brown, white, yellow, purple, orange, and green of all hues. Yes, it is indeed very compact and hard. (I can personally attest to this).
I and my fellow rock hounds have dug mozarkite in Lincoln and found pieces in sizes ranging from small chunks to pieces 10” in diameter. I have cabbed numerous pieces for rings and pendants. I have even cabbed (not knapped) arrowheads from mozarkite. They are not dull gray. These arrowheads have wonderful colors and make beautiful jewelry.
Editor’s Note: You can find photos of jewelry made from mozarkite here.