Supergirl--Action # 262

In this story, Supergirl continues her efforts to find a solution for the problem of Kryptonite. She places a green K meteor in a cave and tries to approach it and marks where she first feels pain. The second day she goes a little closer, and then closer still, till it seems that she must have become immune to the stuff. However, when she attempts to save Superman from Kryptonite she also falls victim to the poisonous radiation. They save themselves by focusing their x-ray vision on some gold above the green K. The gold is transmuted into lead by the effect of their vision, covering the meteor. Later they discover the reason why the other Kryptonite meteor was becoming less painful to Supergirl was that a metal-eating beast was eating the meteor from the inside.