painshill wrote:
Very interesting, Mark. “Cotton rock” is one of those terms that’s used to describe a variety of lithologies. Sometimes it’s used to loosely describe decomposed chert, but most commonly it’s a limestone where 50% or more of the structural calcium has been replaced by magnesium as Calcium Magnesium Carbonate.
That’s certainly what your very impressive item looks like - Magnesian limestone or Dolostone (limestone partially replaced by Dolomite), also known as Dolomitic limestone.
Hardness is generally in the region 3.5 - 4, compared to (say) obsidian at 5 - 5.5 or granite at 6 – 7. It will sometimes flake conchoidally, in which case you can get a decent edge on it without resorting to pecking and grinding. Also it sometimes has quartz sand in the matrix which can signifcantly increase the hardness without adding too much to the weight.
I don’t know about native Americans but in many cultures there is a tradition of celts being made in apparently unsuitable materials as votive offerings. They are frequently found in burial contexts, or in association with shrines.
If you look at the bit it has lots of use. Could not have been heavy duty use because it would have broke.
