The igneous rock classification scheme is closely based on the IUGS scheme but contains many changes to make it simpler, more logical and suitable for arrangement in a hierarchy. These changes have been made in close collaboration with IUGS and many of them will be incorporated into a future revised version of the IUGS scheme. There are sections on nomenclature, discriminant features, fragmental igneous rocks, chemically and/or mineralogically 'normal' crystalline igneous rocks, 'exotic' igneous rocks, fine grained crystalline rocks, qualifier terms and rock names that do not conform with the scheme. The report, newly reformatted and re-released here as BGS Research report RR-99-06, has 34 figures and an appendix listing approved names for igneous rocks.
The hierarchical digital dictionary of the Igneous Rock Classification can be used to check rock names and examine their relationships to other rock types and can be used in conjunction with the report to rapidly access specific information. This can be accessed on-line.