Like 'green' technology?  Currently 97% of the world's 17 rare earths originate from China and they are necessary for catalytic converters that reduce emissions in cars, for computer monitors,  pharmaceuticals and many other things that require these specialty metals.

A New York Times report that says that China is blocking shipments of rare earths to the US and Europe.   China's commerce ministry is denying a report by state-sponsored newspaper "China Daily" that it will cut quotas by 30% next year,  to stop over-mining, or to simply hurt competitors while they subsidize their own green technology with lower prices, which has them in a conflict with the Obama administration, who says they are in violation of WTO agreements.