In the last six months the investing public has been inundated with information about rare earth metals

These are the 17 minerals that are not actually that rare, where global supply is dominated by China (for now) that are vital for defense, electronic gadgets and magnets. So important are these minerals that China recently cut exports but that decision appears to have been reversed as of this writing.

There will be more supply to come on line as the geographic concentration of working mines has become a more visible issue. Molycorp(MCP_), up 248% since its IPO in July, might be the best known company in the category of soon-to- be-operating mine, theirs being in California. It also has deposits in Canada, Australia and Alaska among other places.

This means that China's control of global production, currently around 95%, should decline in the next couple of years reducing the perception of scarcity.

To allow fund investors access to the space Van Eck recently launched the Market Vectors Rare Earth/Strategic Metals ETF(REMX_). As the name implies, it is broader than just the rare earths. With the inclusion of "strategic metals," the fund covers 49 minerals.

The fund has 25 holdings with aforementioned Molycorp not being a very large holding at 4.68%. Some of the larger holdings include Iluka Resources and Lynas Corp from Australia and Thompson Creek Metals(TC_) from Canada which is a molybdenum miner. At the country level, Australia is the largest at 24%, Canada 20%, the U.S. 19% and China 15%.

Quite a few of the stocks in this space have already had fantastic runs. In addition to Molycorp's big lift, Iluka is up 44% in the last six months and Lynas Corp is up 172% in that time frame and there are others with large gains.

Large gains obviously raise questions about whether this space is a bubble in the making, or already a bubble. A couple of years I ago I was asked in an interview whether the then hot solar industry was a bubble. My answer was no for the same reason that rare earths will never be a bubble because this space is too small to be the all encompassing event that tech stocks and day trading were 10 years ago.

From a market standpoint there were dozens of Internet stocks with no earnings with market caps each exceeding $100 billion. The entire market cap of the Rare Earth/Strategic Metals ETF is $25 billion and technically the fund captures two different segments.

As a more anecdotal reference there will be no TV dramas about rare earths like the stock market shows "The Street" on Fox or "Bull" on TNT 10 years ago.

Rare earths and strategics can be a mania where short-term investment demand causes prices of related stocks separate from reality and eventually drop dramatically to align more closely with fundamentals. This has been the case with the solar industry as I thought might be the case when I wrote skeptically about that group early in 2008 and it has not bounced back.

I do not believe the same fate awaits the rare earths even if there is a meaningful price correction. Converting your house to solar might be the right thing to do but for now is not economically viable without massive subsidies. However the needs that rare earths fulfill cannot be fulfilled elsewhere; we are not going to revert to a smart phone-less world as one example.

Anyone interested in a narrow exposure to rare earths and strategic metals needs to expect the fund or any related individual stocks to be a volatile addition to the portfolio but this is a valid segment looking out over the next few years.