Sunday, November 7, 2010

Calcite in Brachiopod Fossils

Examples of calcite crystals forming inside brachiopod fossils.  In this case two different brachiopod fossils are shown.  The first image shows a Platystrophia ponderosa brachiopod from the Ordovician Period of Kentucky.  Two images following are of Orthospirifer brachiopod fossils from the Devonian Period of Indiana.

The rest are of Platystrophia ponderosa brachiopods.  The image make look slightly different in color, lighting and focus.  Two different Canon cameras were used to test close up abilities.  A Powershot Pro in Super Macro mode and an EOS DSLR with a 50mm macro lens.  Incandescent light was used and the DSLR white balance was not set right making the fossils look yellowish.


Steve Finnell said...

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Anonymous said...

The second one appears to be quartz.

Kentuckiana Mike said...

Yes, that probably is quartz since the brachiopods are sometimes found in chert.

What non-destructive ways can I use to determine the difference between calcite & quartz crystals? Is there some sort of optical method to determine crystal structure? Do the crystals react different to certain wavelengths of light?

Ways I can think of testing would be to see if the crystal can scratch glass (if so quartz) or expose to acid to see if it fizzes (if so calcite). The acid test can be destructive and the glass scratch test not always physically feasible.

Dave said...

Take a steel dental pick (Mohs hardness of 5) and see if it scratches the crystals. Calcite (Mohs scale 3) will scratch, quartz (Mohs scale 8) will not.