Jason's Gem is a computer game for the ZX Spectrum in which the hero Jason must make his way through a series of caves in search of the legendary gem of the title. It was published in 1985 by Mastertronic and written by Simon White.
The game begins with Jason docking his spaceship on a moving platform. He then descends through rocky caverns blasting away the rocks as he goes. Upon reaching the bottom of the caves he must negotiate a series of platform screens before reaching his goal and attaining glory.
Source: Wikipedia, "Jason's Gem", available under the CC-BY-SA License.