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Re: eggs with thin shells
Date sent: Wed, 8 Feb 1995 22:19:30 -0500
Send reply to: Crpntr@ix.netcom.com
>From: Crpntr@ix.netcom.com (Kenneth Carpenter)
To: Multiple recipients of list <firstname.lastname@example.org>
Subject: Re: eggs with thin shells
Neil Clark wrote:
>Through compaction the calcite shell can be thinned in the direction of
>maximum compaction resulting in the egg being thinner on the top
>and bottom and thicker on the sides.
>->0<- (egg seen sideways on as I can't find the keys to do it the right
>way - arrows show direction of compaction and the thinned part of the
Sorry, no the calcite of the shell would not thin through compaction, it
would however, telescope in. It is also important to note that shell
thickness is not even all over the egg. It is usually thickest on the
lower pole or bottom, medium on the sides, and thinnest on top to allow
the hatchling out (the French refer to the thin top as the "hatching
window", a term I do not care for).
My reply now.... Yes the egg shell is thinned substantially by
compaction (>25 percent), but not through decalcification directly.
Impacting of quartz grains onto the eggshell surface has caused the
calcite to migrate through pressure solution into the surrounding
sediment. This effectively thins the eggshell on the top and bottom
(at least in the eggs I have dealt with). This produces an un-
oxidised rim to the egg which is green as opposed to red (which is
the colour of most of the surrounding sediment). The sediment is
cemented in these patches by a micrite (fine-grained calcite).
Curator of Palaeontology
University of Glasgow
Mountains are found in erogenous zones.
(Geological Howlers - ed. WDI Rolfe)