More than 70 tonnes of imported zircon sand, a refractory mineral, was ordered on Monday to be returned to its country of origin -- Nigeria -- for exceeding radioactivity standards, authorities said.

The Gamma-ray equivalent of the 74.25 tonnes of zircon sand loaded in four containers was found to be 100 times the normal standard, a Xiamen inspection and quarantine official said.

The zircon sand had been destined for the coastal city of Quanzhou for ceramic production, he said.

Such high level of radioactivity was rare. Importers should set limits on the radioactive standards of minerals, he said.