PURPOSE: To improve the lightweight and heat and fire resistance and enable the obtaining of a glassy sintered compact good in dimensional stability at a low cost by mixing a main raw material composed of sinterable powder and low expandable powder with a lightweight aggregate at a prescribed ratio, then forming the resultant mixture and burning the formed compact.

CONSTITUTION: The glassy sintered compact is produced by providing sinterable powder (A) which is special fine powdery quartz sand having a composition of 80-95wt.% SiO2, 1-5-wt.% Al2O3, 0.1-5wt.% Fe2O3, 0.1-5wt.% CaO, 1-5-wt.% Na2O and 1-3wt.% K2O, glass powder or a mixture, containing ≥5wt.% glass powder and prepared by mixing the remainder of one or more inorganic materials selected from the group of blast furnace granulated slag, silas, etc., therewith, affording low expandable powder (B) selected from the group of spodumene, mullite, etc., subsequently selecting a hollow material such as perlite, providing a lightweight aggregate (C) having ≤0.2 kg/l unit volume, then adding and mixing 0-20wt.% component (C) with 100wt.% main raw material composed of 5-85wt.% component (A) and 15-95wt.% component (B), forming the resultant mixture and burning the formed compact at about 1100°C.