Here is a very colorful stromatolite from the Precambrian of Minnesota. Authorities believe that stromatolites were formed by masses of green or blue-green algae. This stromatolite is from the Biwabik Formation and was found at the Mary Ellen Mine. It is believed that this stromatolite is 2.2 to 2.4 billion years old. This stromatolite slab has been highly polished on both sides to reveal the beautiful colors of the mineral replacement. The different colors and intricate pattern make for a striking display. This is a very pretty slice of an extremely old stromatolite.