Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Mexico-based cement manufacturer Cemex (NYSE: CX) soared like a brick today, falling as much as 18.3% in intraday trading on heavy volume before trading was temporarily halted.

So what: Investors worry that Cemex might not be able to meet its debt covenants, potentially sending the company into a default-fired bankruptcy and share values to absolute zero. Over the last five years, the Dow Jones Industrial Average (INDEX: ^DJI) has dropped a measly 7% while Cemex got a 91% haircut -- and may go even lower from here.

Now what: Once a seemingly bulletproof market darling, Cemex and its industry peers were hit very hard by the worldwide financial crisis of 2008. The Chinese construction industry no longer props up a global glut of concrete-pouring capacity, and there's no end in sight to this misery. Even if Cemex can sell off $1 billion of non-core assets and keep the debtors at bay for a while longer, it's just a question of time before they come a-knocking again. Fellow Fool Sean Williams is slightly more optimistic about the company's future, though; read his take before dumping your shares on my advice.

Interested in more information about Cemex? Add it to My Watchlist.

Fool contributor Anders Bylund holds no position in any of the companies discussed here. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool is investors writing for investors.