The objective of this program was to design, develop, and laboratory- test a breadboard-prototype version of a pocket-sized coal mine dust incombustibles content meter. This instrument was designed to assess the combustibility of coal mine dust deposited on mine surfaces, without the need for sample retrieval, by placing the sensing face of the device directly in contact with the surface of the dust layer. The operation of this instrument is based on the detection of gamma radiaton backscattered by the dust layer under scrutiny. The design of the device was aimed at extreme compactness, incorporating a single-chip cmos microprocessor. The sensing configuration is based on an americium-241 source and a cadmium-telluride gamma radiation detector. Automatic calibration using standard samples and a digital readout directly in percent incombustibles are designed to minimize operational complexity.