Abstract: Dense coherent composition of matter composed essentially of, on a weight basis, 10 to 30% aluminum-base metal phase finely interspersed throughout a mass of substantially submicron size crystals of at least 60% magnesium aluminate spinel, 0 to 10% alpha alumina, 0 to 2% mullite and 0 to 5% magnesium aluminum boride. Made by bringing molten aluminum-base metal at 650.degree.-850.degree.C. (only up to 750.degree.C when MgO content of the base composition noted below is less than 8%) into contact with a mass of melted and solidified material consisting essentially of, analytically by weight, at least 65% being a base composition and 0 to 35% B.sub.2 O.sub.3, the base composition consisting of 5 to less than 40% MgO, 5 to 43% Al.sub.2 O.sub.3 and 35 to 85% SiO.sub.2. Upon contact, metal reacts with mass to transform a substantial portion of the mass into the cermet composition of matter. May be used in form of abrasive grain and/or abrasive articles.

Abstract: Dense coherent composition of matter composed essentially of, on a weight basis, 10 to 30% aluminum-base metal phase finely interspersed throughout a mass of substantially submicron size crystals of at least 60% magnesium aluminate spinel, 0 to 10% alpha alumina, 0 to 2% mullite and 0 to 5% magnesium aluminum boride. Made by bringing molten aluminum-base metal at 650.degree.-850.degree.C. into contact with a mass of melted and solidified material consisting essentially of, analytically by weight, at least 65% being a base composition and 0 to 35% B.sub.2 O.sub.3, the base composition consisting of 5 to less than 40% MgO, 5 to 43% Al.sub.2 O.sub.3 and 35 to 85% SiO.sub.2. Upon contact, metal reacts with mass to transform a substantial portion of the mass into the cermet composition of matter. May be used in form of abrasive grain and/or abrasive articles.