I know from long experience that drywall often (always?) has glass fibers (fiberglass) mixed in with the Gypsum to add strength. Because of the number of drywall related products that have fiberglass in them, I am having trouble finding good references.
I did find Possible Environmental Concerns with Recycling Gypsum Drywall which says Type X drywall has fiberglass in it. The article also says older drywall may have Asbestos and/or Mercury.
Looking for reliable references that indicate how I can tell that a drywall product only has Gypsum between the paper, or at the very least how to reliably identify drywall that has fiberglass or other hazardous additives.