Classifications and Historical Studies is a collection of papers dealing with theoretical and applied ore petrology. One paper discusses the use of conceptual models in geology such as the diagrammatic/pictorial, the flow-chart, and the tabular types of conceptualizations. Another paper describes some transitional types of mineral deposits in volcanic and sedimentary rocks. Concentrations of copper minerals and commonly associated metals form deposits associated with orogenic belts and cratonic regions. The paper points out that many major groups of mineral deposits grade into other groups through occurrences with intermediate or transitional characteristics. It suggests a classification method of mineral deposits based on the observable features of the mineral deposits rather than their inferred genesis. One paper reviews the theory of magmatic—hydrothermal replacement origin of stratiform sulfide ore bodies. The review covers concepts of certain major ore deposits as being independent and isolated phenomena to regarding a wide range of deposits as contemporaneous, indigenous, and related to their environments. Another paper points out that according to North American geologists, certain types of ore deposits are formed syngenetically and are subjected to the same metamorphic events that affect the ores in which they are enclosed. The collection can be valuable to researchers, technical designers, or engineers whose works are related with oil refinery and fossil fuels, as well as to students majoring in geology.