I have the vague idea that metal originally meant anything dug up rather than specifically what we now call metals. So stones from a quarry were also "metal".

The Latin and Greek dictionaries in Perseus would seem to confirm this. The Latin metallum and Greek metallon both meant mine or quarry (and the products thereof).

Latin: http://makeashorterlink.com/?Y597127A4
Greek: http://makeashorterlink.com/?J1B7227A4

Bingley

Bingley