iron carbonate

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.
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.