Sven is quite right. To expand on his comments:

In an article in American Paleontologist a few years ago, I said that if you
look here in New York State on the barrier island beaches, as well as
finding marine mollusk shells from animals that died this week or this
month, you can also find shells from animals that died anything from a few
years ago, hundreds of years ago, or even a few thousand years ago. These
shells had been buried in the sand deposits until they got washed out again.

On those same beaches you can also find numerous shells that have just
recently washed out of sand deposits that date from the late Pleistocene,
about 10,000 years ago, or more than that. Most of these shells are the
exact same species as the ones that live here now, although a few of the
species you can find now only live much further south.

These Pleistocene-age shells technically count as being "fossil", but they
are very hard to tell from the more recent shells, especially those shells
that are, for example, just a few thousand years old and are considered to
be "sub-fossil".

On our local beaches, the fossil (and subfossil) shells are usually more
dull and opaque inside than the Recent shells are, and they are often faded
and slightly discolored. In addition they never have any periostracum or
ligament.

However, these features are NOT ones that a person could always use in order
to try to tell a fossil shell from a Recent shell. As Sven says, in many
circumstances there is no simple and reliable way to tell a fossil seashell
from a Recent seashell, especially when the specimen is out of its original
context.

Susan

Susan J. Hewitt
Citizen scientist, research on mollusks
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435 East 77th Street, Apt 3G
New York, NY 10075, USA
212 ­ 628 - 6706
Affiliated with the American Museum of Natural History


On 1/4/14 7:50 AM, "nielsen" <[log in to unmask]> wrote:

> Dear Chandrashekhar Phadke.
>
> Carbonate shells usually remain carbonatic, only that aragonite often
> recrystallizes to calcite. Sometimes there is no way to distinguish them
> except by their geographic and/or stratigraphic context or direct
> dating. That still leaves the question when is a fossil a fossil?
>
> Sven Nielsen
>
> Am 2014-01-04 05:33, schrieb chandrashekhar phadke:
>> Dear friends ,
>>
>> How to distinguish between the fossil seashells and the normal
>> seashells ? Whether fossil seashells give effervescence reaction to
>> the acid ? If during fossilization, calcium is replaced by some other
>> elements it may not give acid reaction. Would like to have comments
>> from the experts.
>>
>> Chandrashekhar Phadke
>
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