The planet Mars tantalizes with its resemblance to parts of Earth. Now space geologists with their trusty field assistant, the rover Opportunity, have found gypsum veins there like those in our own countryside.
Sand . . . we play in it, we stroll on it, we make castles out of it, but what do we really know about it? The size, shape and location of a grain a sand can tell us a lot about it's origin, makeup and history.
Check out this Google map that shows clay minerals found around the U.S. and world that are commonly used in pottery.