The energy of sticking out in a rounded form (not a spike) is a crop, the craw or crop of a bird, and, because the rounded heads of grain can be gathered in a hand and harvested together, a group. In that case, a crop is an active force, and holds that force within itself. Wherever crops land, they form a group.
A crop (or group) of granite stones. Adding more or taking all away except one would not reduce or expand their energy.
The word lives on in the geological term “out-cropping”, but has also grown to include cap, cup and cob, and from that cobblestone, among many others. These head words differ from the related throat words, creek, croak, and crack, which are inward. Interestingly enough, streams running through cracks can tumble and even create crops of stones. They can even arrange them into groups. This is the language of mountains and streams, but also of narrow throats and open mouths. To look at language, look to the rocks.