THE PLT WAS ADVISED BY SPRINGFIELD TOWER THAT ICING CONDITIONS EXISTED ALONG HIS PROPOSED ROUTE OF FLT. HOWEVER, HE ELECTED TO TAKEOFF, & ABOUT 4 MIN LATER, THE PLT ADVISED THAT HE HAD ENCOUNTERED RIME ICE. HE CONTINUED THE FLT TO JOPLIN, PICKING UP MORE ICE ALONG THE ROUTE. AT JOPLIN, THE PLT MADE AN ILS APCH TO RWY 13 WITH PLANS TO CIRCLE & LAND ON RWY 31. WITNESSES SAW THE ACFT PASS OVER THE FIELD, HEADING SOUTHEAST, ON THE RIGHT SIDE OF RWY 13. A SHORT TIME LATER, THE ACFT CRASHED WHILE THE PLT WAS MAKING A CIRCLING APCH. IMPACT OCCURRED IN A LEFT WING LOW, NOSE LOW ATTITUDE. ANOTHER PLT WHO LANDED A FEW MIN BEFORE THE ACCIDENT REPORTED THAT HIS WINDSHIELD WAS 3/4 OBSCURED WITH MIXED ICE & THE WINGS OF HIS ACFT HAD ACCUMULATED 1/4 INCH OF CLEAR ICE ON THE LEADING EDGES. HE SAID THE ICE ACCUMULATED IN 6 TO 10 MIN IN THE PRECIP AREA.