Remember The Commodity Bubble That Exploded In 2011?

People love to talk about bubbles.

In the markets today there seems to be near-constant hand-wringing about whether we're in a bond bubble now, or if the Fed is inflating a stock bubble, or if there is a bubble in student loans.

And while it remains to be seen what the future holds for these assets, there is at least one asset class we can look to in not-too-distant past and say yes, that was a bubble, and boy did it pop: rare earth elements.

Back in 2010, rare earth elements were supposed to be the "can't lose" investment of the decade. Rare earth elements are hard to mine and are used in a wide variety of consumer products like plasma TVs, magnets, and high-efficiency light bulbs.

But despite the seemingly obvious supply-demand dynamic driving up the price of rare earth elements, eventually the price bubble in these commodities got inflated quickly and deflated aggressively.

And now, Molycorp, one the largest rare earth mining companies, is teetering on the edge of penny stock status, while the price of rare earth elements has recovered just slightly.

Assets might get expensive and then sell-off, but next time you go calling something a bubble, keep this chart in mind. This is a real bubble.