So what could it be? The high-resolution MAHLI camera is intended to snap close-up observations of Mars surface features - acting like hand lens magnifiers used by geologists in the field. Therefore, the object - that, as noted by Boyle, is shaped like a tiny ‘flower' - is pretty small.
Naturally, the ever-optimistic and irrational part of my brain wants this to be evidence of some kind of Mars fossil, but in all likelihood, it's a concentration of minerals embedded in the rock. The former may sound more exciting, but the latter is the most likely explanation.
The human brain often attaches significance to random shapes, concluding that if it looks like a flower on Mars, then it must be something biological. This is a psychological phenomenon known as "pareidolia" - and Mars is a very fertile environment for fooling our brains with random shapes.
So, we should wait until Curiosity's mission scientists have a moment to analyze the object and, if necessary, command the rover to take a closer look. We're only just scraping the surface of the red planet, there's plenty mysteries to come...