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Date: | Thu, 27 Sep 2018 20:21:00 -0600 |
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All comments have been passed on, thank you.
Tom
On 9/27/2018 10:18 AM, David Campbell wrote:
Yes, drying is an important factor. It also depends on how it's being
measured and what type of shell - is the measurement based on amounts of
carbonate, or of calcium, or what? Different measurement techniques
have their advantages and disadvantages. Echinoderms have rather higher
magnesium levels than mollusks. Aragonitic mollusks will have more
stray strontium mixed in, and calcitic mollusks will have more stray
magnesium mixed in. Is there periostracum present? How is the shell
treated in the preparation for analysis? etc. True nacre (mother of
pearl, not merely smooth and shiny) has more organic matrix than
standard non-nacreous shell mineralogies. Corbulids have layers of
conchiolin the shell, apparently making it harder for drilling predators
to get through. Some shells can have a tiny amount of vaterite, a third
crystal form of calcium carbonate.
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