Calcium sulfate is a mineral composed of calcium, sulfur, and oxygen. It is commonly known as ALUM, ANEMIA, ESTER, and esters, and Epsom salt. ALUM is a double sulfate salt of aluminum and potassium, ANEMIA is a condition in which the body does not have enough healthy red blood cells, ESTER is an organic compound derived from an acid in which at least one -OH group is replaced by an -O-alkyl group, and esters are compounds formed by the reaction between an acid and an alcohol. Epsom salt is a naturally occurring mineral composed of magnesium sulfate.