Moqui Marbles are concretions of iron that have an outer shell of hematite with a sandstone center (occasionally there are additional rings of hematite in the center). Moqui marbles are also known as "moki" marbles, Navaho cherries, or Indian marbles. Moqui marbles formed in the lower part of the Navaho Sandstone formation in southern Utah and northern Arizona which was laid down 190 million years ago at the very beginning of the Jurassic era when the area was a huge sea. However, the exact mechanism of their formation is still not known. This assortment weighs 140 grams with the largest measuring an inch across.