This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
礩 combines 石 (stone) with 質, which likely contributes the sound. The exact historical development is uncertain.
The left side is stone 石, and the right side is 質 (substance, quality). Picture a stone of uncertain quality, its meaning unclear.
For シツ, imagine a stone sitting quietly: sit -> シツ, and the stone's meaning remains a mystery.