Impressive 2.4 BYA Stromatolite - Rare Girvanella Form

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 stromatolite is at once, ancient (Precambrian), beautiful, and unusually colored. Coming from the Chocolay Group in an area know 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 colors close to orange, lavender, and various tans, among others - rather like butterscotch in areas.

This particular specimen is a verticle cross section that has a multiple individual bacterial colonies of an unsymmetrical spherical form called Girvanella (sometimes called algal balls, though I dislike this misleading nomenclature, since eukaryotic algae had not yet appeared in the lower Proterozoic). A large, partial structure is in the upper left, a medium, complete structure in the middle right, and a number of smaller forms in the lower portion. Such specimens are very rarely able to be found and produced. Because of its shape and patterns, we nickname this form "butterfly wing" based on its obvious resemblance.

At 10 by 8 inches, the plaque is unusually large and therefore difficult to cut and polish.