Description: This banded iron is metasediment
(sediment that has undergone metamorphism) and has a high content
of magnetite (Fe3O4), making it a natural magnet, also resulting
in the midnight black coloration. Mminute crystalline forms of other
mineral-based compounds are also present; Whether the sediment was
of bioorganic origin (stromatolite) is indeterminable, but likely.
The
specimen has been hand-polished to a glassine finish on one side
with fine carbide and diamond abrasive, a very labor-intensive job.
The reflected colors of the polished side highly
depends on the angle of reflected light. Depending on angle, colors
vary from black to gray and red to silver. This is a very pretty
example of banded iron that portrays a defining event in geological
history and evolution: the rusting of the earth due to bacterial-produced
oxygen that also led to the creation of atmospheric oxygen. At the
time this banded iron was formed, the earth had been rusting for
about 1.5 billion years, and about another 500 million years would
be required before the process exhausted the marine iron supply. |
