Gypsum and toothpaste!
Gypsum is a common ingredient in toothpaste. Gypsum, also known as calcium sulfate dehydrate, is used in toothpaste as a mild abrasive to help remove plaque and surface stains from teeth.
In addition to its abrasive properties, gypsum can also help to strengthen teeth and reduce sensitivity. It is safe for use in toothpaste and has been approved by regulatory agencies such as the U.S. Food and Drug Administration (FDA) for use in oral care products.