Here is a detailed paper describing CheMin, a neat X-ray lab for MSL capable of identifying almost any mineral.

http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1608.pdf

Chemin now has its own homepage, with more technical detail.

NASA also has a short feature on it.

There also a press article which gives some more background. Interestingly it says that Chemin has been part of two proposed Discovery missions (one to a comet, another to the moon). Does anyone know which missions they are?