China's exports of rare earth metals burst through the $100,000-per-tonne mark for the first time in February, up almost ninefold from a year before, while the volume of trade stayed far below historical averages.

China's squeeze on rare earths, which are used in a wide range of hardware including precision-guided weapons, hybrid car batteries and iPads, has forced prices up dramatically since July last year, when each tonne fetched a mere $14,405 on average.

The apparent price rises have averaged $10,000 per tonne per month but accelerated in February, galloping ahead by $34,000 per tonne, according to Reuters calculations based on data from China's Customs office.

Last month each tonne of exports was valued at $109,036 on a free on board basis, almost half as much again as the average value in January.

The explosion in export values has coincided with a collapse in volumes coming out of China, the source of almost all the world's rare earth supplies, which has cut export quotas of the 17 rare earth metals and raised tariffs on exports.

China's actions have infuriated its trading partners but lifted the shares of the few mining and prospecting companies outside China that are well-placed to capitalize on the constriction of Chinese supply.

They include U.S. miner Molycorp Inc, Canada's Rare Element Resources and Neo Material Technologies and Australia's Arafura and Lynas.

But those firms' share prices have been under pressure this month because Japan's earthquake and tsunami are expected to temporarily slash demand from China's biggest customer. In February, 281 tonnes of Chinese exports went to Japan, valued at $38.9 million or $138,406 per tonne.

China exported a total of 750 tonnes in February, slightly more than the 647 tonnes shipped in January but otherwise the lowest monthly volume since February 2009, when demand was hit by the global financial crisis.

China's Customs office changed its method of presenting rare earths exports in its headline data this year, boosting the reported volume by including products made from rare earth metals in the total.

By that method, exports were 2,976 tonnes in February, up by 132 percent from a year before, when the figure did not include rare earth products.

(Reporting by Tom Miles)