KDE has it built in to default key binding of Ctrl + Meta + Esc helpful when in Wayland as xkill only works on X and xwayland apps.

Likely glaciation, the bottom rock was likely on the bottom of an ice sheet and millions of tons of ice moving over it over time had smoothed it out.

The top rock is probably from many miles away and was carried and placed there from the receding glacier. To me the top rock looks like it is a completely different type of stone then the bottom.