Chiang didn't touch the tomb. Sun Dianying, a Chinese warlord, had his troops ransack the tomb for valuables. It is said that Sun Dianying offered said pearl to Chiang Kai-Shek as a gift but I don't know of any evidence of this. However I will say that Chiang was known to be pretty austere even by his detractors and the lack of evidence otherwise makes me suspect this is mostly rumor. Especially as Sun Dianying was opposed to Chiang politically.