Jiongtao,

I am leaving this on the list so others can jump in and point out any errors
I may make.

I believe the reason the subfossil shells are in such good shape is that
they are buried.  Once buried the shell is protected from oxidation and
erosion.  A dead shell that is not buried will quickly have all of the
things happen to it that "ruins" the shell for collectors.  Worms,
barnacles, corals, sponges, etc. will build on it and chemically it will
begin to breakdown (much faster for a gastropod than something like a oyster
because of the material used to make the shell).  If the shell happens to be
anywhere near wave action it will also be abraded by wave action in the
sand.  I saw an experiment once where a cowrie completely lost its gloss in
less than an hour or so of wave action in beach sand.

Anyway, all of this is avoided or slowed way down if the shell is buried.
Once the shell is buried, the lack of oxygen stops other critters from
building on it and slows down the destructive chemical processes that will
ruin the finish.  However, "slows down" is not stopped, and the shell does
change.  As you have seen from the shells you got from Don Pisor, the colors
fade even though the glossy surface remains intact.  That glossy surface is
a protective coating on the shell and continues to function even after the
animal is dead.  You can find fossil Cypraea and Oliva from millions of
years ago that are pretty much grey in color but the glossy surface is still
there.  In fact, if you are interested I can send you a couple -- I don't
think I have any extra Cypraea but I am sure I have an Oliva around here.
Write me off line at [log in to unmask]

Tom Eichhorst in New Mexico, USA


>But I wonder why these "subfossil cowries" have excellent
> glossy surface and without any worm holes. Most of they have beautiful
> colorations.