Infrared transparent mullite (3A12O3•2Si02) was formed at 1250°C through densification of monolithic gels. The gels were prepared through colloidal mixing of boehmite (A100H, aluminum monohydroxide) and tetraethoxysilane (TEOS). After four hours at 1250°, monolithic gels densified to 98% of the theoretical density (TD). Densification was promoted by viscous phase deformation of silica (Si02) during sintering. The extent of densification was found to be dependent upon the extent of agglomeration of boehmite powder in suspension. Transparency in the infrared region was obtained as a result of mullite formation in the sintered product. The microstuctural evolution during densification and the concomitant spectral transmittances were characterized.