When can the Zakat due on minerals be discharged?

Primary text

It is not permissible to discharge the Zakat on minerals until after they have been smelted and purified. The amount due is one-tenth (one-twentieth if calculating after purification, which is contrary to the ruling on grains). If one extracts one-fortieth of the raw earth (before purification) as Zakat, it must be returned if it still exists, or its value must be compensated if it has been destroyed.