Pual;
        That was one totally SMASHING answer!  Just want to compliment you (and
several other lerned members of the list) on your contributions to the
conchological community: you are so generous in sharing what you know. Thanks.

-Ross.


          Paul Monfils wrote:

Hello Linda,

"Lime" deposits on shells and other hard surfaces exposed to the marine
environment are generally not deposited by simple chemical
precipitation.  Such material, while largely inorganic in composition,
is typically biological in origin, deposited by a variety of organisms,
both macroscopic and microscopic.  The larger organisms include those
you mentioned - corals, barnacles, tubeworms, and others, including
molluscs.  The predominant microscopic forms are bryozoans and coralline
algae, but various other types of organisms may contribute, such as
encrusting foraminiferans, and even the spat of sessile bivalves like
Ostreidae, Spondylidae, and Chamidae.  If the calcific material is
freshly deposited, structural detail can often be seen with a low power
microscope.  Bryozoans often create interesting, intricate patterns,
superficially resembling microscopic corals.  However, such material,
once deposited, is subject to ongoing erosion, and old deposits are
often worn smooth, just as old dead coral
often is.

Regards,
Paul M.