This paper documents the development of an expert system for rock mass classification for use on microcomputers._ The expert system called R. MC was develoOed using an expert system shell FLOPS. FLOPS is a shell based on the Al language OPS5 with many unique features. The system RMC utilizes most of these unique features. Among the features used are approximate reasoning with fuzzy sets, the blackboard architecture and the emulated parallel processing of fuzzy production rules. Details of the development of RMC including discussion of some relevant fuzzy set backgrounds are described in this paper.