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Re: Blackboard Chalk

Actually it is neither of these materials.  Blackboard chalk is made from
the very tiny (less than 5 microns diameter) critters called coccoliths
and they are calcite which is CaCO3 in a hexagonal form.

Just being a "prig" or trying to fulfill by duty to the list.
o    Mike Nielsen                                                        u 
m    Department of Geography         THE OPTIMIST BELIEVES WE LIVE IN    ? 
a    Harvill Bldg Box #2             THE BEST OF ALL POSSIBLE WORLDS;    w
r    Tucson, AZ 85721                THE PESSIMIST FEARS THIS IS SO      h 
e    mnielsen at u_arizona.edu