This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
碿 combines 石 (stone) with 屑, but the historical origin and original meaning are uncertain. It may have been a phono-semantic compound, but the exact development is unclear.
The stone radical 石 beside 屑 suggests something related to stone or grinding, but the exact meaning is unclear.
For ソツ, imagine a stone (石) being used to grind something into small bits (屑), making a 'sots' sound: sots -> ソツ.