Moqui Marbles are spherical rocks with a hematite shell and sandstone interior. These marbles can range from the size of a pea up to the size of a basketball. Even though they are called Moqui Marbles, They are not all spherical. Moqui Marbles are a brownish black color on the outside and the inside can be a tan orange color or yellow and red. They may also show a concentric structure. The way the hematite shell is formed is that there is iron in the sandstone, when it is combined with oxygenated water, the oxygen meets the iron it has a chemical change, which creates a new iron mineral known as hematite. The hematite is cement like coat that covers sandstone.This mostly found in areas where sandstone is bleached.