Anhydrite is a naturally occurring mineral composed of calcium sulfate with the chemical formula CaSO₄. It belongs to the sulfate mineral group and crystallizes in the orthorhombic crystal system. The gemstone variety of Anhydrite is known as Angelite, which is especially valued for its soft and calming blue color. Unlike gypsum, which contains water in its structure, Anhydrite is an anhydrous mineral, meaning it does not contain water molecules. Angelite typically appears in pale blue to deep sky-blue shades, although Anhydrite itself can also occur in white, gray, violet, or colorless forms. The blue coloration in Angelite is caused by trace impurities and specific environmental conditions during its formation. It usually has a dull to vitreous (glass-like) luster and is often opaque to translucent in appearance, giving it a smooth and soothing visual appeal.