The three types of crystal faces

The [hkil] faces, which determine the dog-tooth (scalenohedral) Habitus of calcite crystals, and the prismatic [hkil] face of tourmaline crystals show striations only, never step patterns. These faces are S faces, by PBC analysis, and they appear due to a pile up of steps developing on the neighboring F faces. Yet they develop as large as those that determine the Habitus. 

Crystal faces with curved or wavy surfaces, not exhibiting either striations or step patterns, are rarely encountered. In most cases, these faces appear by dissolution. Rough interfaces grow by the adhesive-type growth mechanism, their normal 

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