Before remote or autonomous mining machines can improve upon the performance of current man-machine systems in terms of mineral recovery, safety, and productivity, suitable environmental sensors must first be developed. The U.S. Bureau of Mines is addressing one facet of the problem relative to keeping an extraction machine within the coal seam through its coal interface sensor research. This paper reports on the performance evaluation of a coal inteface detector developed by the General Electric Company. That uses the vibrational response of the machine to distinguish between cutting coal and rock. The evaluation was performed under contract by Wyle Laboratories through an extensive field and data collection effort that spanned four mines, four different longwall shearing machines, and three different coal seams. Results of the study indicated that the general electric detector was not effective in identifying the material being cut.