For instance, I'm unclear whether people would have been aware, at the time, that Sapphire was an oxide (or at least decomposable - because contemporary confusions about oxygen). Might Lavoisier have been aware but an interested lay person not aware?
Basically I'm looking for a plausible for circa 1790 argument that Sapphire is an element that is framed with reference to Lavoisier's treatise.
I've read the wikipedia pages on Lavoisier, Sapphire, Corundum and Chemical Nomenclature. I've searched on "Méthode de nomenclature chimique", "Sapphire history", "Sapphire history chemistry", "Corundum History"