I was reading that story Sandra posted a couple of days ago. "Destroy" is too strong a word; stones may be altered by the appearance of carbon on their surface, but a grassfire isn't going to destroy stone. The "burn scar" is a temporary area where fire took out the brush and grass.

This island once had forests. If forests return and they burn it probably wouldn't destroy rocks, though if there was a prolonged fire in a deep fuel area it could crack them.

I worked in forestry for a number of years and was around a lot of fires at that time. The life of that island is probably improved when fire passes through, releasing more nutrients into the ecosystem. The rocks may look a little different but the char may wash off.