This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鑙 is a rare character of uncertain origin. It combines 金 (metal) with a complex right-side component that may have contributed sound, but the exact historical development is unclear.
With 金 (metal) on the left and a dense right side, imagine a hard, unyielding metal object that resists shaping—fitting the kun-reading かた.い (hard).
For ケイ, picture a metal key (ケイ) that is so hard it cannot be bent: key -> ケイ, and the metal radical reinforces the image.