"Chester Lake" - Sol 2709 (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunar Explorer Italia)

Caption NASA:"An Outcrop informally named "Chester Lake" is the second rock on the Rim of Endeavour Crater to be approached by NASA's MER Opportunity for close inspection with instruments on the Rover's R.A. This view of Chester Lake combines images taken during the 2709th Martian Day, or Sol, of Opportunity's work on Mars (such as Sept., 7th, 2011).
Chester Lake is about 3 feet (1 meter) across. It lies on the inboard (South/Eastern) side of a low ridge, "Cape York", which forms a portion of the Western Rim of Endeavour Crater. Rover team scientists chose it for inspection because it is in-place bedrock that appears to be representative of a region of Outcrops on the inboard side of Cape York.
Chester Lake differs from the first rock inspected by Opportunity on the Endeavour Rim, "Tisdale 2", which is a Boulder excavated during an impact event that produced a small crater on the Rim. Both rocks appear to be "Breccia", a type of rock fusing together broken fragments of older rocks.
By Sol 2713 (Sept. 11, 2011), researchers had used Opportunity's Microscopic Imager and Alpha Particle X-Ray Spectrometer to study Chester Lake and were planning to use the Rover's RAT (Rock Abrasion Tool) and, possibly, its Moessbauer Spectrometer on the rock. They will use all the data to reconstruct the chemistry, mineralogy and geologic setting of Chester Lake, including evidence about whether or not the rock has any clay minerals in its composition".