A Splinter of the Minds Eye.
Original Star Wars スター ウォーズ novel
I bought it in the UK in 1978.
Tells the (unfilmed) story of Luke & Leia as they search the planet Mimban for Kaiburr crystals whilst being hunted by the Imperial army and Darth Vader.
Originally written as a low budget sequel to Star Wars - in the event that the original film was not successful enough to finance a high budget sequel.