Superboy's First Kryptonite

Back in the 1950s and 1960s, there was Kryptonite everywhere on Earth for Superman to encounter. 

But, one of those encounters had to be the first!

So, let's travel back to the time when Superman was a boy in Smallville, and let young Clark Kent tell the tale of his first encounter with green Kryptonite under this Curt Swan/Stan Kaye cover!

Superboy's Last Day

It was related in Adventure Comics #251 (August, 1958, by Otto Binder and George Papp), as a nostalgic Superboy related the tale of a day like any other day, as he worked on a geology project for school.  Pa Kent brought home a glowing green rock for Clark to see, yet, as Clark Kent suddenly developed his first illness when he came home, Pa forgot to tell him about it.  The illness would come and go as Superboy left the house, yet every time it came back even worse.  If not for one of Superboy's earliest robots (who was lead lined), Clark wouldn't have figured out it was the rock (which they would dub Kryptonite) that was causing his illness.

Oddly, the DC Calendar puts this event as happening on August 5th, yet, the calendar on the Curt Swan/Murphy Anderson Superboy #165 (May-June, 1970) has it as August 4th (take it as the day Clark got sick to when he found out it was the rock...), with the Kryptonite flashback being set for "seven years earlier", around the time of Adventure Comics #170.