Pearson symbol

The Pearson symbol, or Pearson notation, is used in crystallography as a means of describing a crystal structure, and was originated by W.B. Pearson. The symbol is made up of two letters followed by a number. For example: The Pearson symbol, or Pearson notation, is used in crystallography as a means of describing a crystal structure, and was originated by W.B. Pearson. The symbol is made up of two letters followed by a number. For example: The two (italicised) letters specify the Bravais lattice. The lower case letter specifies the crystal family, and the upper case letter the centring type. The number at the end of the Pearson symbol gives the number of the atoms in the conventional unit cell. IUPAC (2005) The letters A, B and C were formerly used instead of S. When the centred face cuts the X-axis, the Bravais lattice is called A-centred. In analogy, when the centred face cuts the Y- or Z-axis, we have B- or C-centring, respectively.