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.

       As of Oct. 1, exporters must provide the authorities with detailed, step-by-step tracings of how shipments of rare earth metals are used in Western supply chains. That has given Beijing greater authority over which overseas companies receive scarce supplies.

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       China is also taking greater corporate ownership over the mining and production of the metals. In a deal that has received almost no attention outside the country, the last two foreign-owned rare earth refineries in China are being acquired by one of the three state-owned companies that already run the other refineries in China.

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       A worker stood back as flames leaped out of the oven where rare-earth-based chemicals are roasted for more than 20 hours.Credit...Ryan Pyle for The New York Times

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