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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