The effect of heating quartzite from room temperature to 650 degrees C in 1 h then quenching in various aqueous media has been investigated by two different methods. Operating work index tests were used to determine the effect of this process on the grinding energy required for size reduction of the material over an hour of milling. Ultra-fast load cell (UFLC) tests were carried out to determine the effect of the process on the specific fracture energy E and the particle strength sigma(p) of the material prior to milling. The UFLC tests showed that the aqueous media quenches caused a significant reduction in both E and sigma(p), compared with the untreated material; acid, alkali and salt solution quenches caused further reductions in these values compared with water-only quenching. The operating work index tests showed that aqueous quenching reduced the grinding energy required for the first 30 min of milling, and this effect was still noticeable after 60 min of milling in the case of acid, alkali and salt solution quenches. The two independent test procedures have established the effectiveness of this process for weakening quartzite.