said that Kryptonite is a compound made up of 15.08%  plutonium , 18.06%  tantalum , 27.71%  xenon , 24.02%  promethium , 10.62%  dialium , 3.94% mercury , and 0.57% of an unknown substance. A Post Crisis story in  Action comics #591  (Aug 87) also made Kryptonite a compound. [ edit ]