What is a rare metallic element of which little is known. It is said by Scacchi to have been extracted from a yellowish incrustation from the cracks of a Vesuvian lava erupted in 1631 called?

vesbium — A rare metallic element of which little is known. It is said by Scacchi to have been extracted from a yellowish incrustation from the cracks of a Vesuvian lava erupted in 1631. (Webster's 1913.)