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 a multiplicity
of 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 right, and numerous medium to small structures
are dispersed about. 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
more than 10 by 8 inches, the plaque is unusually large and therefore
difficult to cut and polish.
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