This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
礆 combines 石 (stone) with 僉, which likely contributes the sound. The exact historical development is uncertain.
The stone radical 石 suggests a rocky or mineral connection, but the overall meaning is unclear. Picture a mysterious stone tablet with the complex shape 僉 carved into it.
For ケン, imagine a ken (a Japanese unit of length) of stone: ken -> ケン, and the stone radical 石 reinforces the image.