FORTUNE — Tantalum is a rare element in high demand. To control tantalum is to control a key part of the 21st-century supply chain: Half of all tantalum mined goes into electronic capacitors, which store an electric charge. And it is expensive — $130 per pound, vs. its rarer cousin, tungsten, at $28. Here’s what you need to know.

What it is

A metal on the periodic table, tantalum is nonreactive and won’t corrode, making it good for surgical equipment, implants, and aircraft engines. A little bit of tantalum holds a lot of electrical charge. “It is not easily substitutable,” says Bryan Ellis, CEO of Global Advanced Metals, the biggest supplier of tantalum.

Where it’s mined

Brazil (26%), Australia (12%), and Mozambique (17%), according to Merchant Research & Consulting. Last year rebels took control of several tantalum mines in the Democratic Republic of the Congo; the government response cut 10% of the global supply.

Why it’s expensive

Supply is erratic; demand is only increasing. Plus, Dodd-Frank legislation requires suppliers to document where their metals come from, adding as much as 2% to the final cost, says Kay Nimmo of the Tin & Tantalum Supply Chain Initiative.

Who it’s benefiting

Capacitor suppliers AVX (AVX) and KEMET (KEM). Both companies sell to Intel (INTC) and Motorola. Global Advanced Metals recently shut down its massive Wodgina mine in Australia owing to production costs, which will cause a price increase.

This story is from the October 8, 2012 issue of Fortune.