Subject:  Natural Geological formations of the Sahara Desert
   Last year, in a Cairo curio shop, I purchased five naturally formed
spherical stones. They appear to be white marble or alabaster; they
are a little smaller than a tennis ball and weigh about 2 lbs each.
They are very smooth and white to whitish-gray in color. Please tell
me something about them, as I cannot find any information in my google
search. Do that have some mystical significance?

This newsgroup thread may be of interest to you:

http://groups.google.com/groups?hl=en&lr=lang_en&ie=UTF-8&oe=UTF-8&newwindow=1&safe=off&th=5b081ec44ae7a575&rnum=1

The description suggests that these are calcium carbonate concretions,
similar to those found elsewhere in the world, which form in
sedimentary rocks. Such spherical concretions can become quite large.
See:

http://www.state.nd.us/ndgs/ndnotes/concretions/concretions_h.htm

Note: the pictures take a while to load.

hlabadie-ga