Cyrtospirifer, also called large ‘Swallow Stone’, is a common traditional Chinese medicine. It is a type of fauna fossil composed of minerals such as calcite and aragonite. Cyrtospirifer fossils are mainly preserved in the Late Devonian strata and are widely distributed around the world. In China, Cyrtospirifers are mainly found in the limestone and mudstone in the Upper Devonian Xi Kuangshan (Tin Mining Hill) Formation in Hunan Province. They are also mined in the Upper Devonian marl, limestone and dolomite. Because of erosion, individual fossils are often scattered on the surface. Clusters of large and complete fossil pieces have a very ornamental value.