Lower Proterozoic Stromatolites from Michigan

Description: Precambrian stromatolite is the oldest of all fossils, and with much labor (cutting and polishing), it is most beautiful. The banding that commonly appears in stromatolite is a record of the growth patterns of colonies of microorganisms, principally photosynthetic cyanobacteria. The colors that are often expressed are the result of the interaction of biological and sedimentary processes, together with subsequent chemistry and mineral exchange.

This stromatolite is at once, ancient (Precambrian), beautiful, and unusually colored. Coming from the Chocolay Group in an area known as the Chocolay Hills located southeast of Ishpeming, Michigan, it dates to the Lower Proterozoic, some 2.2 to 2.4 Billion years old. This stromatolitic carbonate has been hand-polished to a mirror finish, and the delicate pink color is due to the presence of rhodochrosite, a manganese carbonate mineral. It has been colloquially termed butterscotch.