This is the VOA Special English Economics Report.

Few people had ever heard of the natural elements known as rare earth metals before a recent dispute between China and Japan. Yet these metals are used in devices like smartphones, flat screens, hybrid car batteries, MP3 players and military equipment.

In September, Japan detained a Chinese ship captain near disputed islands in the East China Sea. China denied that it stopped exports of rare earth metals to Japan to force his release. But the incident raised concerns.