Baryte (BaSO4) is a mineral consisting of barium sulfate. The name baryte is derived from the Greek word βαρύς (heavy). It is generally white or colorless, and is the main source of barium. Barite is the unofficial American spelling. The mineral is also called heavy spar or tiff. The radiating form, sometimes referred to as Bologna Stone, attained some notoriety among alchemists for the phosphorescent specimens found in the 1600s near Bologna by Vincenzo Cascariolo. Its Mohs hardness is 3, the refractive index is 1.63 and it has a specific gravity of 4.3-5. Its crystal structure is orthorhombic.
Baryte commonly occurs in lead-zinc veins in limestones, in hot spring deposits, and with hematite ore. It is often associated with the minerals anglesite and celestine.
Most crude baryte requires some upgrading to minimum purity or density. Baryte that is used as an aggregate in a "heavy" cement is crushed and screened to a uniform size. Most baryte is ground to a small, uniform size before it is used as a filler or extender, an addition to industrial products, or a weighting agent in petroleum well drilling mud.