Moqui Marbles, Hematite Spherule n3-3,5cm

This rocky ball is not just a concretion of sandstone and hematite, its also evidence that water once existed on Mars. These concretions commonly form in the Southwest United States and were called Moqui Marbles by the Hopi people who have lived in the area for thousands of years. When iron-bearing minerals weather, the iron molecules seep into the groundwater and oxidize with other granules. Over time, as the surrounding stratum erodes, it exposes the spherules and they collect on the surface. This natural process may sound boring, but it became a geological hot topic when Opportunity found similar spherules on Mars. The Martian spherules, initially called blueberries, stumped scientists when first discovered, but eventually the connection to the terrestrial version was made.