A powder including: (a) more than 92% of zircon particles, (b) 1% to 2% of silica particles having a size less than 50 microns; (c) 0.3% to 5% of particles comprising one, two, or three oxides selected from CaO, MgO, and Y2O3; (d) less than 1% of particles comprising other oxides; the powder also being such that it includes: more than 5% of zircon aggregate particles having a size greater than 1 mm; and 8% to 20% of zircon matrix particles having a size less than 15 μm and including, for more than 95% of the weight thereof, a monoclinic phase.