The vise-tight grip that China wields over the mining and refining of rare minerals, crucial ingredients of today’s most advanced technologies, is about to become even stronger.

In a series of steps made in recent weeks, the Chinese government has made it considerably harder for foreign companies, particularly semiconductor manufacturers, to purchase the many rare earth metals and other minerals mined and refined mainly in China.

Already, China produces almost all the world’s supply of these materials. The new restrictions solidify that market dominance.