Abstract: A building panel comprising, when completed, a substantially rigid polyester resin building mass in sheet form having molded therein a plurality of closely compacted porous scoria rock particles of varied size in range of 1/4 to 11/4 inch diameter size and each comprising vesicules of varied size in range of 0.1 to 0.5 millimeters diameter that occupy the major portion of the volume of each such particle, such particles being compacted to form a substantially incompressible mass, said polyester resin being of substantial tensile strength and extending between the rock particles and including fingerlike intrusions extending into the larger vesicules of the rock particles and holding the rock particles together, said compacted rock particles substantially filling the entire volume of the polyester resinous mass, and including portions extending beyond the volume occupied by such polyester resin mass.