Assuming that the stone has not been dyed, carnelian is the
traditional name used to describe the red to reddish brown variety
of cryptocrystalline quartz (agate). While there IS an
internationally recognized procedure for the naming of MINERALS, no
such thing exists for variety names of gem and near-gem and lapidary
material, much of which is rock and not mineral. This seems to cause
quite a bit of confusion among people who are not directly involved
in lapidary, but just be aware that one man's red agate could be
another man's carnelian.
Many times, the reddish component of carnelian, sard, sardonyx,
brownish red agate, reddish brown agate, whatever you wish to call
it, can be intensified by heating, which alters the iron causing the
coloration. At one time, the predominant source of fine carnelian was
actually the United States! Even today, one can find excellent
material along the banks of Newaukum Creek in WA state (and
elsewhere, see Sinkankas' Gemstones of North America), where it
weathers out of the soil banks. Private property, ask for permission
first. August-Sept best time for the hunt. (It's a bit of a hike).
And if it's red like the red in the flag, it's dyed. Of course, it
cold be a beautiful brownish red and still be dyed, too. Usually,
there is no quick and easy way to tell, it's often a matter of
having handled a lot of material, but that's no guarantee, either.
If you have a concern for owning/using an un-dyed piece, you could
work directly with a lapidary shop and have the material cut without
any intervening treatment. And they won't know and can't tell if it
has been heat treated after "mining" unless they dug it out of the
Carnelian (also commonly called sard or sardonyx) has a long history
in cultures around the world. Many fine examples exist in
Mesopotamian and Egyptian jewelry and it was commonly used for seals
in Roman times. Aaron's breastplate, etc.....