Bravais rule

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Bravais rule (Bravais law) Crystals are formed by the repetition in three dimensions of a unit-cell structure defined by lattice points in space. The Bravais rule (proposed by M. A. Bravais) states that the density of these lattice points, or spacing between lattice planes, is proportional to the relative importance of crystal forms. It follows that the faces most likely to be found on a crystal are those parallel to lattice planes of greatest point density.