Collenia Form of Proterozoic Stromatolites from Michigan

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 prokaryotes (e.g, 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 particular specimen exhibits a rare structure for stromatolite, the so-called "Collenia" form genus comprising many small dome structures that has a pattern rather resembling a topological map. 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 on one side exhibits intricate banding and a spectrum of reddish-brown colors.