Re: Info on Type of Pebble?


Mardon wrote:
My daughter found the pebble shown at:
http://www.JustPhotos.ca/misc/images/pebble.jpg
It was lying on the ground near Dryden, Ontario, Canada (N49.807º,
W92.856º). Can anyone tell us about the nature of this pebble that
has a light coloured core, inside the harder, darker shell? There
was nothing similar to be seen in the area but I guess we wouldn't
have noticed this one either if it had not been already split in two.
Thanks for any comments offered.

Years ago I visited a gravel pit in the Sudbury area where these types
of rocks are abundant. It was located along the road leading to
Fairview Lake. I have a specimen that looks very similar to the one
shown in your photos. Similar rocks, containing concretions and
concentric structure, also occur in gravel pits in southern Ontario.
Some claim the internal concentric structure in pebbles was due to
weathering. I think the concretionary development occurred during an
in-situ disintegration process, related to unloading due to erosion of
overburden, that changed rocks into gravel.

Doug

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