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.