There isn't one specific word for a break between rock formations. The best word depends on the type of break and the context. Here are some possibilities:

For a general break:

* Fracture: This is a general term for any break in a rock.

* Fissure: A narrow crack or opening, often extending deep into the rock.

* Joint: A fracture in rock where there has been no movement along the fracture.

* Fault: A fracture in rock where there has been movement along the fracture.

* Crevice: A narrow opening or split in a rock face.

* Gap: A space or opening between two things, including rock formations.

For a break caused by erosion:

* Canyon: A deep, narrow valley with steep sides, often carved out by a river.

* Gorge: A narrow, deep valley, often with steep sides, formed by erosion.

* Ravine: A deep, narrow valley, typically formed by erosion.

* Chasm: A deep, steep-sided fissure in the Earth's surface.

For a break caused by geological processes:

* Fault scarp: A cliff created by movement along a fault.

* Dyke: A vertical sheet of solidified magma that has intruded into existing rock.

* Sill: A horizontal sheet of solidified magma that has intruded between layers of existing rock.

The most appropriate word will depend on the specific type of break and the context in which you are using it.