Mars just keeps throwing up surprises: the Curiosity rover has imaged a metallic-like protuberance emerging from a rock:
Visible in the image above, the protuberance appears to have a high albedo and even projects a shadow on the rock below. The image was taken with the right Mastcam on Curiosity on Sol 173 — January 30, 2013 here on Earth...
...the protuberance seems different than the rock on which it sits – it could be composed of material more resistant to erosion than the rest and similar material could be within the rock, or it could be something that is “grown” on the rock. However, it looks fairly smooth, and in fact it is not covered by dust as is the case for metal surfaces that tend to clean easily.
But “small” is the operative word here, as the little protuberance is probably about 0.5 cm tall, or even smaller.
The full image from NASA/JPL can be found here.