“The Curiosity Mars rover has imaged a small metallic-looking protuberance on a rock. Visible (in the image below the green lines point to it), 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 – (see the original raw image here), and was pointed out to us by Elisabetta Bonora, an image editing enthusiast from Italy. See a close-up of the object below.

As Bonora pointed out, 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”. – UniverseToday.com