Alum means many things to many people. To most people, alum means hydrated aluminum sulfate, which is the salt of sulfuric acid (a strong acid) and aluminum hydroxide (a weak base). Alum is also known as papermakers' or filter alum.
Almost all the alum produced in the United States today is manufactured from bauxite, bauxitic clays and other clays, which are found primarily in Alabama, Arkansas, Georgia, and Missouri. Deposits are also located in Jamaica, Guyana, Surinam, and other South American countries and in Asia.