Acid maceration is a technique used to extract organic-walled microfossils or kerogen from rock. A rock sample is cleaned to remove external contamination and crushed into small pieces. About 25 mg is macerated in chlorhydric acid solution (HCl) to remove carbonate minerals, rinsed with distilled water, and then macerated in fluorhydric acid solution (HF) to remove silicate minerals. A following step of boiling the macerate in hot HCl removes fluorides formed during the previous acid step. This protocol may vary according to the nature of the rock, of the fossils, and of their degree of preservation. After neutralization of the final macerate with distilled water, the residue is filtered on sieves of desired size fractions, then mounted on microscopic slides or kept in vials for other analyses.