crack

Great rock monoliths such as Half Dome and El Capitan in Yosemite, or Stone Mountain in Georgia, are not in fact monolithic—they are riddled with fractures, which are known as cracks or joints in the parlance of climbers and geologists. Mountaineers categorize cracks according to the size of the body part that can be effectively wedged into a given crevice to enable ascent—that is, a finger crack has the dimensions of a finger; a hand crack is the width of a jammed hand; and a fist crack conforms to the span of a human fist. When a crack is broader than fist size but narrower than a chimney, it is known as an off-width, and can be very difficult to climb. In certain types of rock (most notably Wingate Sandstone and some varieties of granite) cracks may be astonishingly uniform and run for hundreds of feet without interruption; such perfect fissures are termed splitters.

Jon Krakauer