This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
磶 combines 石 (stone) with 舄, which likely contributes sound. The exact historical development is uncertain.
The stone radical 石 suggests a connection to rocks or foundations, but the overall meaning is unclear.
For セキ, imagine a stone (石) that makes a sharp 'seki' sound when struck: seki -> セキ.