insoluble residue (in-sol'-u-ble). The material remaining after the more soluble part of a rock sample has been dissolved in, e.g., hydrochloric acid or acetic acid. It is chiefly composed of siliceous material (e.g. chert or quartz) and various detrital minerals (e.g. anhydrite, glauconite, pyrite, and sphalerite). Abbrev: IR. See also: siliceous residue.