1. . 
A high-specific gravity and finely divided solid material used to increase density of a drilling fluid. (Dissolved salts that increase fluid density, such as calcium bromide in brines, are not called weighting materials.) Barite is the most common, with minimum specific gravity of 4.20 g/cm3. Hematite is a more dense material, with minimum specific gravity of 5.05 g/cm3, per API and ISO specifications. Calcium carbonate, specific gravity 2.7 to 2.8, is considered weighting material but is used more for its acid solubility than for density. Siderite, specific gravity around 3.8, has been used to densify mud, but can cause problems by dissolving into the mud at high pH. Ilmenite, specific gravity of 4.6 has been used in drilling fluid and cement. Only barite and hematite have API/ISO standards.
Synonyms: weighting agent