Growth of Crystalline Solids from Liquids

Planar crystal surfaces that survive during crystal growth are the slowest growing facets the fastest growing ones disappear entirely in the evolving crystal 

Dendrites form if solidification is limited by diffusion. The dissipation of latent heat can be the rate-determining factor. As heat conduction is better in the liquid than in the solid phase, there is spatial anisotropy in the solidification rate and the solid assumes a ramified shape. Latent heat is more easily disposed of at the end of the dendrites than in depressions on the growing solid surface, and the tops of dendrites grow faster than the depressions in the surface. This positive feedback yields the same type of morphology as diffusion-limited aggregation, which is 

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