The shatter cone page

Shatter cones are conical fractures with typical markings produced by shock waves, and they belong to the regular macroscopic shock inventory in rocks of impact structures.

Shatter cones, negative and positive, in Malmian limestone, Steinheim impact structure (Germany).

They have been observed in rocks shocked in explosions of nuclear tests and have experimentally been produced in the laboratory. The required shock pressure is estimated between roughly 20 and 200 kbar (2 and 20 GPa). In general, the apex of the cones points to the shock source, but irregular orientations and even counter orientation (see image above) are frequent. In impact structures, the size of the cones is between centimeters and meters. Fully developed cones are rare which is explained by rock inhomogenities. In the extreme, shatter cones may degenerate into shatter cleavage (in slaty rocks).

The typical horsetail markings of shatter cones remind of fracture markings of the plumose or hackle type (also see Roach, D.E., Fowler, A.D. & Fyson, W.K. 1993: Fractal fingerprinting of joint and shatter-cone surfaces. Geology, 21, 759-762.)

Plumose fracture markings in Solnhofen limestone (left) and detail (right).

A significant similarity between shatter cone fracture markings and markings from a plane fracture in a strongly anisotropic material, potassium chloride KCl, is shown below. In both cases, the fracture propagation is from SE to NW.

Fracture markings in a KCl crystal (left, modified from Ernstson & Schinker 1986; the field is 2 mm wide) and horsetail fracture markings of a shatter cone (negative; Malmian limestone, Steinheim impact structure).

The idea that the typical plumose fracture markings develop in anisotropic materials, has been published in a paper by Ernstson & Schinker (1986; see list of references). From the completely identical inventory of plumose fracture markings in rocks and cleavable crystals, the authors conclude that plumose structures originate from an advancing fracture front in closely spaced planes of weakness in an anisotropic material. Likewise, it is assumed that the shock front produces conically shaped anisotropic zones of weakness (shear zones) in which fractures propagate to produce the “horsetail“ shatter coning by shuttling between neighboring planes of weakness.

The following images show shatter cones with varying features from different impact structures. Special emphasis on shatter cones from the Azuara and Rubielos de la Cérida impact structures (Spain) is given at the end.

[top]