Disclosed is the preparation of sintered cordierite-based glass-ceramic bodies via a procedure which uses three all natural starting materials which are white sand, kaolin clay and magnesite. These three raw materials are combined in relative amounts which form, upon subsequent mixing and heating, a specific mixture of oxides of silicon, aluminum and magnesium. Upon melting at 1500-1550° C., this combination of raw materials forms transparent brown glass which after solidification by quenching is then crushed and reduced to grains having a median particle size less than 65 microns. These brown glass grains are consolidated, for example by compaction, to form a green body for sintering. Sintering of the green body at temperatures between about 1000° C. and 1375° C. for from 2 to 5 hours produces glass-ceramic bodies containing a polycrystalline material which comprises mostly material of the cordierite crystal structure.