They tend to form in vertical or near-vertical faces of rock.
They can be as little as 0.1 m to several metres in height, width, and depth, with arched-shaped entrances,concave walls, sometimes with overhanging hoods or visors, especially in case-hardened rocks (rocks with a surface made harder by the local mobilization and reprecipitation of minerals on its surface),and smooth and gently sloping, debris-strewn floors.
Some tafoni cut right through boulders or slabs of rock to form rounded shafts or windows.
The origins of tafoni are complex.