Fig. 3.

Anticracks: their nature, appearance, and explanation. (a) Cartoon showing idealized shape and orientation of anticracks in the stress field that caused them. Extremely rapid nucleation of a more dense phase in a less dense one leads to nanocrystalline lenses of the daughter phase that orient themselves normal to maximum compressive stress and develop very large compressive stresses at their tips. See text for discussion of analogy to fluid-filled cracks. (b) Anticracks filled with nanocrystalline spinel produced in olivine. (c) Thermodynamic explanation for anticrack formation (see text), modified from ref. 10.