The difference in the two sets of rocks may not be immediately obvious to the layman. Yet given Leonardo’s passion for geology and his genius for painting, closer evaluation suggest that the
Louvre rocks are Leonardo’s and the National Gallery’s are not.
Leonardo’s observational geology is far more accurate than the geology of Renaissance theorists. Such extraordinary knowledge provides us with an unbiased method of distinguishing his work from that of his many imitators and followers. Precise geology is an index to authenticity. It can serve as Leonardo’s inimitable trademark. As we continue to examine his work from this perspective, as I hope to do in future studies, we can be relatively sure that no other artist of his time understood geology so well.