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Normal fossilization is when biological remains break apart at different rates and rock and sediment fill in the games, leaving behind a sort of picture of the original thing "color coded" by what it was made of. A Rock type Pokemon is made of living stone and wouldn't gradually wear away and be replaced by sediment since it's already sediment. So any Rock Pokemon fossils are the original biomatter of the Pokemon and not normal rock.
The "revival" process is just an extension of Pokemon center healing on a Pokemon that fainted long ago.
