Guardian Of The Crystal Gate

Robert Silverberg actually wrote Guardian Of The Crystal Gate based on this cover.

“In fact, after I had been part of his staff for six months or so, he paid me the considerable compliment of asking me to write a story around a cover painting that Ed Valigursky, one of his best artists, had just brought in.
The painting showed two attractive young ladies in short tunics fiercely wrestling atop a huge diamond.”

You can read the whole thing here

via via