Abstract: The invention is an improvement in conventional processes for the production of fire-resistant products from naturally-occurring magnesium orthosilicate-rich rock with fine-grained addition of a magnesium oxide-containing substance, and optionally of a chromium oxide-containing substance, wherein the resulting granular mixture is introduced into a formed body and then calcined at sintering temperatures to provide the product, the improvement comprising adding the magnesium orthosilicate-rich starting material in an amount such that the product obtained has a mole ratio of magnesium oxide to silicon dioxide of 1.64:1 to 1.85:1, and sintering the product sufficiently to achieve a gross density of more than 2.80 g./cc.