Where does “скала́” come from?

скала́ (Russian) comes from Proto-Slavic skala, from Proto-Slavic skoliti — to cleave, to split.

Ancestry of “скала́”, step by step

Step	Language	Word	Meaning
1	Proto-Slavic	skala	crack, cleft → sliver, fragment, wedge; rock
2	Proto-Slavic	skoliti	to cleave, to split

скала́ — Etymology, Origin & Word History | Etymology Explorer