Older Strombus spp are also darker or cloudy on the lower side. This is
because, as they move about, the sand abrades the surface of the shell,
which is uncomfortable for the animal (do you like to sleep on scratchy
sheets?). It then secretes more shell material, which is just slightly
opaque. The older the animal, the thicker the material and the more opaque
it gets. Sometimes it even looks black, and those shells are called SAMBO
phase, at least in Caribbean shells.

Occasionally algae will grow on the surface before the animal lays down
more material, and then the green color is fixed in between layers of shell
and will not come off.

I wouldn't be surprised if this is the process making older cowries cloudy
as well.

Peggy Williams

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                                  Peggy Williams
                                   Shell Elegant
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                                Tallevast FL 34270
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