Barite is often used during drilling operations to increase the density of water based drilling fluid. It's used to "weight up the mud". This is necessary for well control purposes. Barite is commonly chosen due to its low reactivity and affordability.

Ba"rite (?), n. Min.

Native sulphate of barium, a mineral occurring in transparent, colorless, white to yellow crystals (generally tabular), also in granular form, and in compact massive forms resembling marble. It has a high specific gravity, and hence is often called heavy spar. It is a common mineral in metallic veins.

© Webster 1913.