BGS Rock Classification Scheme

The BGS Rock Classification Scheme (RCS) is a corporate standard setting out a practical, logical and robust system for classifying and naming geological materials as they appear at the scale of a single exposure, hand specimen, or thin section.

Classification helps to place materials in a wider geological context, and allows unambiguous and informative formal names to be assigned.

The RCS provides a comprehensive system for classifying and naming geological materials to act as a corporate standard in support of our digital geological maps, data dictionaries, and numerous other modern geological applications.

In addition to the four rock classification volumes, a scheme for the classification of discontinuities is now available.


To use this dictionary, please enter the name or part-name of the rock type that interests you; then click the "Search now" button.

You can also search by the code if this is known. Searches can be carried out using one or any combination of the code and description.

Search the BGS RCS

Download the 4 volumes of the BGS Rock Classification scheme

Volume 1 Igneous rocks 663KB pdf More about igneous rocks
Volume 2 Metamorphic rocks 260KB pdf More about metamorphic rocks
Volume 3 Sediments and sedimentary rocks 459KB pdf more about sedimentary rocks
Volume 4 Artifical man-made ground and natural superficial deposits 3.1MB pdf More about superficial deposits
BGS scheme for classifying discontinuities and fillings 4.04MB pdf More about discontinuities and fillings

Principles of the BGS Rock Classification Scheme

  • classification is based on descriptive rather than interpreted attributes
  • classification is based on what rocks are not what they might have been; some flexibility is allowed for metamorphic rocks
  • in general it should be possible to classify a rock from features observable in a hand specimen or thin section; it should not be necessary to see field relationships
  • types or groups of rock types are defined by boundary conditions that will generally follow natural or well established groupings
  • well-established rock names are retained wherever possible although some terms are more rigorously defined
  • the scheme is essentially hierarchical
  • rock names are assigned using a system of approved root terms and qualifier terms


The rapidly increasing use of computers to store geological information and the production of maps from these databases has also driven the formulation of these schemes. Computers can integrate data very rapidly from a wide range of sources from properly constructed databases but it is vital that the data are input with a consistent meaning. This requires a clearly defined comprehensive rock classification scheme with master dictionaries of all the approved rock names.


Hard copies are available on request. Contact the Keyworth Sales Desk for prices.