Join Date: Feb 2008
Location: In a California Ghost Town
^^^ Chalk is made from coccolithophores, which are protists, and therefore neither plant nor animal. Foraminifera also compose a substantial quantity of limestone deposits, and they also protists too.
I don't have a problem with using fossilized animal remains though. I give my animals a supplement made from fossilized coral calcium. Its that or bone meal, and I don't want to use bone meal made from modern animals.