Say you want to invest in the coal sector, but you want a little more volatility and exposure to higher prices? Alpha Natural Resources (NYSE:ANR) might be a company to consider. While one of the smaller publicly traded coal companies out there, Alpha has above-average exposure to high-value markets like clean(er) Appalachian coal and metallurgical coal.

Unfortunately, it's not really possible to talk about second-quarter results in great detail. Because of some uncertainty on the treatment of an accounting idea, the company has delayed presentation of full results. That doesn't mean that we are completely without information, though.

Based on the midpoint of management's range, revenue rose approximately 18% this quarter, as overall production increased 24% and sales volume rose 12%. Hurting results somewhat would have been the spread in the coal sales -- steam coal volumes were up 25% this quarter, but metallurgical volumes were down 8%.

With the uncertainty of the aforementioned accounting item (which pertains to the recognition of purchases and sales of coal) and the impact of stock option expense, there wasn't a particularly clean earnings number, but the guidance provided suggested a modest shortfall, as did the company's guidance toward the lower end of its earnings target range for the year.

As I said, Alpha is a smaller company -- the second smallest in reserves of the eight companies I routinely follow, and about one-fifteenth the size of Peabody (NYSE:BTU) on a BTU-equivalent basis. And though it does have above-average production costs, that is mitigated by a large relative volume of high-value metallurgical coal, as well as reserves of Appalachian coal that contain comparatively less sulfur than average. Moreover, the company takes an approach somewhat similar to Powder River Basin coal specialist ArchCoal (NYSE:ACI) in that it has fairly significant uncontracted volumes in the coming years.

In some respects, Alpha is a play on some direct subthemes within coal. As James River (NASDAQ:JRCC) could be considered a leveraged play on Illinois Basin coal, Alpha is a play on cleaner Appalachian coal and metallurgical coal. If emission allowances begin trading up again and/or the steel market stays strong, that'll bode well. If new scrubbers and pollution control technologies lower the value of those allowances and/or steel softens, that could be problematic for the company's pricing.

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Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).