Geology can't explain this one! What appears to be a manufactured metallic object, rectangular in shape and hollow on the inside, has been found on Mars in Gusev Crater. No, geology doesn't purify metals and shape them rectangularly. Everything on Mars is not a rock.
This animation shows the two color images from sol 1419 and 1420 of the object:
This one is referred to as the "cowbell," or sometimes, the "ammo box." The video below shows the general area around the cowbell so that you can see how this object stands out in comparison to nearby objects:
Image credit: NASA/JPL. http://marsrovers.jpl.nasa.gov/galler...
The cowbell object was found by the Spirit rover in Gusev Crater on sol 1419, and brought to our attention on the Hidden Mission forum by Maya. RetiredAFB discovered the tire shaped object. Special thanks to RetiredAFB, Maya, and Keith Laney's The Hidden Mission forum.
Raw Images Courtesy of NASA and ESA. Special thanks to EVERYONE who has contributed in the search for Mars anomalies. Also thanks to Google, Picasa, ImageShack, and Photobucket.