Opportunity has spotted a possible meteorite on the surface. The rock is called "Block Island," and was discovered on July 18, 2009.
Here is a mosaic that I produced from the RAW image website.
And below is an RGB composition that I constructed from the RGB data at the Exploratorium RAW data website, (RGB process for correct colour balance).
Credit: Exploratorium
Courtesy NASA/JPL-Caltech.
You may have noticed that I've changed the close-up colour picture a few times. I'm still trying to find a definitive guide for processing colour Mars images.
This is the closest that I can get, using the histogram readings from the image calibration target.