Now, don't quote me on this, but I think I rememner reading that it was either a copper alloy or a form of red granite. I know I read it in Charles
Berlitz ATLANTIS, but I can't be too sure as to what the speculation was.
Originally posted by Pisky
The sestertius, a coin worth four asses and dupondius, worth two asses were both struck in orichalcum brass ...
An alloy of copper and zinc called orichalcum was used a great deal by the Romans. This consisted of eighty percent copper and twenty percent zinc, with small amounts of lead, tin, and other metals and would be called yellow brass today.
Bronze, Brass and Orichalcum
I have a Sestertius of Antoninus Pius - so there is Orichalcum within 10 feet of where I am sitting.