Interesting to know. I occasionally find shells (almost always small) in this condition, and I also wondered about the time involved. I shell in the vicinity of Guaymas, Sonora, Mexico.

---- "Powell wrote:

=============
With the right conditions this can happen very fast - within a year, but
just because the shell still has color doesn't mean it isn't thousands of
years old.  Since the preservation isn't similar to any others found at the
same site I would guess its older than you might think.

Best,

Chuck


On Tue, May 28, 2013 at 4:40 PM, Susan J. Hewitt <[log in to unmask]>wrote:

> Those of you who pick up marine mollusk shells on tropical beaches may
> have come across the
> phenomenon of gastropod shells washing up that are not fossil, but that
> are partially filled with really
> hard cemented sand.
>
> I have seen this in shells from one locality in the Bahamas, and this year
> I found a small rare muricid
> shell on St Kitts, Leeward Islands, that still had color and was in
> relatively good shape, but was half
> filled with hard cemented sand. No other shells that I found on that beach
> were like that.
>
> I am assuming this is a natural process (the same process that creates
> “Coquina” rock) and that it
> means that the shells thus affected are not fresh, and are probably some
> years old...but the question
> is, do we have any idea how fast can this happen, and thus how long this
> might mean that the shell
> has been lying around for...? A year or two? Decades? Centuries? Any
> ideas? Any guesses about how
> fast this could happen?
>
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--
Charles L. Powell, II
U.S. Geological Survey, MS 975
345 Middlefield Road
Menlo Park, CA  94025

1-650-329-4985
https://profile.usgs.gov/cpowell/

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