The invention relates especially to a mixture of grains and particles of fused vitreous silica produced by dry mixing: (i) a moderately coarse particle size fraction of fused vitreous silica, (ii) a fine particle size fraction of fused vitreous silica, in which at least 95% by weight of the grains are smaller than 40 .mu.m, (iii) substantially spherical particles of fume silica, and (iv) optionally, at least one particle size fraction of fused vitreous silica which is coarser than fraction (i), the constituents (i) to (iv) being employed in the following proportions by weight: (i) 15-70%, (ii) 15-55%, (iii) 3-15% and (iv) 0-52%. The mixture can be used for the production of articles made of sintered vitreous silica.