Acid maceration is a technique to extract organic microfossils from a the surrounding rock. HCl or acetic acid may be used to extract phosphatic fossils, such as the small shelly fossils, from a carbonate matrix. HF is also used in acid macerations to extract organic fossils from silicate rocks. Fossiliferous rock may be immersed directly into the acid, or a cellulose nitrate film may be applied (dissolved in amyl acetate), which adheres to the organic component and allows the rock to be dissolved around it.