PEWTER IN ANCIENT TIMES This silvery grey metal is chiefly derived from cassiterite (which takes its name from the Isles Cassiteriti, thought to be the Isles of Scilly, southwest Cornwall). Tin is mainly found in underground ore deposits, tied together with other minerals, but it is also found in sand as placer deposits. As native element, tin is rare. It is said to be first extracted in Central Asia. The extraction of it in south-west Britannia was described by Diodoro, Caesar's contemporary: "