|  These
stromatolites are banded iron from the rusting of the earth. Unusual
for banded iron is the intricate wavy laminae structure resulting
domal growth. Coming from the Goldman Meadows Formation in Wyoming
it Archaean in age, when life on earth was highly diverse, but
all microbes.
This
banded iron is metasediment (sediment that has undergone metamorphism)
and has a high content of magnetite (Fe3O4), a natural magnet,
and yielding the midnight black coloration; minute crystalline
forms of other mineral-based compounds are also present.
The
very large specimen has been hand-polished to a glassine finish
on one side with fine carbide and diamond abrasive, a very labor-intensive
job. The pictures comparing front and back reveals the value of
this form of polishing in revealing the fine structure of the
laminae. | 
