Friday, August 24, 2012

Flint: Sedimentary Quartz

Flint is a variety of a sedimentary rock called chert. Chert is composed primarily of micro-crystalline quartz and can be many colors, but when it contains a lot of fossilized algae it becomes black and is called “flint.” Technically any chert that is black or toffee-colored is called “flint.”
Flint is formed when calcite in limestone is replaced by silica, thus flint is often found with limestone or even contained within a limestone shell (This can be seen in the first picture) In Kentucky’s Mammoth Cave large nodules of the stuff are found poking out of the cave’s limestone walls! Flint has a glassy texture and breaks with a conchoidal fracture like obsidian. Flint is amorphous, meaning that it has no distinct shape, but it is often found as lumps. Many years ago flint filled the Y and T-shaped tunnels of ancient creatures, so casts of this form are sometimes discovered.
Because of its conchoidal fracture, flint can be used to make bladed tools such as arrowheads and has been used in this manner since ancient times. Flint produces sparks when struck with carbon-steel and has been used as a fire-starter. Flint was also used with flintlock guns. The hammers of these firearms held a piece of flint and when the trigger was pulled the flint struck a steel plate, which ignited the powder and caused the gun to fire.
Many books have listed England as a source of flint. Germany and Denmark are also considered sources. Flint Ridge, Ohio contains the rock and I have found good specimens in central Kentucky. Based on what I understand, flint can be found in many other places, but I cannot name any other specific sources.

No comments:

Post a Comment