Three Top Terms are provided - 'Organic', 'Inorganic' and 'Processed Material' and are generally mutually exclusive. 'Organic' is defined as naturally occurring animal and plant material, and naturally occurring substances derived from them. 'Inorganic' is defined as naturally occurring material which, for the purposes of this thesaurus, is not of organic origin, i.e. mainly minerals and stones. 'Processed material' may be regarded as material which has been manufactured or has undergone some form of processing (such as smelting) to alter it from its original natural state. The definitions of the three categories are provided for general guidance, rather than as strict formulations. It is accepted that there are grey areas, particularly in deciding whether a substance is processed or not. However the primary intention is to group materials in a way which is meaningful to the average user. 2129 terms, 513 relations between terms, 284 non-preferred terms. It is stressed that the final listing is not intended as a scientific classification system, rather it is a reflection of the terminology, both current and historical, in use in curatorial departments in The British Museum."