A sound-insulating lightweight ceramics with pseudo-open porosity was obtained from calcite-zeolite rock using energy-saving procedure. A thorough analysis of chemical processes occurring during material preparation revealed that decomposition of CaCO3 with extensive gas release destroys cellular structure of thermally softened material. The latter, however, can be overpassed by proper alkali activation, which leads to transformation of CaCO3 into sodium carbonates (like trona and thermonatrite) with lower decomposition temperature. The reported results suggest that quality lightweight ceramics with sound-insulating properties can be obtained even from poorly zeolitized rocks with high CaCO3 content previously treated as unsuitable for such application.