A low‐power diffractometer with a microfocus x‐ray tube with the focus on its window is described. X‐ray paths are kept short and the whole of the diffracted cone enters the detector, which leads to an improved sensitivity as compared to conventional instruments. For the most intense quartz line, sensitivities of 920 counts per second per microgram have been obtained at a tube power of 1.25 W and Cr radiation. Specimens of less than 50‐ng quartz can be detected. The low power results in low weight, less than 20 kg, thus allowing the instrument to be portable.