gypsum <p>Naturally occurring soft white mineral that is commonly used as a retarding agent in portland cement, as a core in sheets of wallboard, as a white pigment, in grounds for paintings, and is the main component of alabaster.</p> <p>Source: AAT</p> <p><a href="http://vocab.getty.edu/page/aat/300011099">http://vocab.getty.edu/page/aat/300011099</a></p>