1. n. [Drilling Fluids]

A mineral composed of ferrous carbonate, FeCO₃, and having 3.8 g/cm³ specific gravity. It is found as an accessory mineral in some shales and carbonate rocks and also in some barite and hematite ores. FeCO₃ is readily soluble in acids and breaks down slowly in alkaline muds, particularly at high temperature to form a gelatinous solid, Fe(OH)₂, and soluble CO₃^–2 anions.

Reference:
Binder GG, Carlton LA and Garrett RL: "Evaluating Barite as a Source of Soluble Carbonate and Sulfide Contamination in Drilling Fluids," Journal of Petroleum Technology 33, no. 12 (December 1981): 2371-2376.

See: alkalinity,  carbonate,  carbonate test,  caustic extraction test,  colloidal solids,  Garrett Gas Train,  iron sulfide,  pH,  pyrrhotite