No diamond has ever been found in native Missouri rock. It is possible
for diamonds to have been carried into the state with the glacial
deposits in the northern part, but the probability of finding one, if it
did come in, is extremely remote.
Diamonds do occur in one part of Arkansas, but those rocks are
strikingly different from all Missouri rocks except in a few localities,
having small areas about the size of one’s house, in the southeastern
part of the state. The writer has received quartz and calcite crystals
for testing from persons who hoped they might be diamonds. It is almost
a foregone conclusion that diamonds do not occur in Missouri.
A diamond may be recognized by its extreme hardness. It is the hardest
substance known, natural or artificial, and will scratch any known
substance; but it, in turn, is scratched only by another diamond. Acids
do not affect diamonds in the least.