The Pearson symbol, or Pearson notation, is used in crystallography

Crystallography

Crystallography is the experimental science of the arrangement of atoms in solids. The word "crystallography" derives from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write.Before the development of...

 as a means of describing a crystal structure

Crystal structure

In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...

, and was originated by W.B. Pearson. The symbol is made up of two letters followed by a number. For example:

• Diamond structure, cF8
• Rutile structure, tP6

The two (italicised) letters specify the Bravais lattice. The lower case letter specifies the crystal class, and the upper case letter the lattice type. The figure gives the number of the atoms in the unit cell. IUPAC

IUPAC nomenclature of inorganic chemistry 2005

The Nomenclature of Inorganic Chemistry, IUPAC Recommendations 2005, commonly known as The Red Book, is a collection of rules for naming inorganic compounds, as recommended by the IUPAC.- Summary :...

 (2005)

Crystal class

a	triclinic
m	monoclinic
o	orthorhombic
t	tetragonal
h	hexagonal and rhombohedral
c	cubic

Lattice type

C	Side face centred
F	All face centred
I	Body centred
R	Rhombohedral
P	Primitive

The fourteen possible Bravais lattices are identified by the first two letters:

Crystal class	Lattice symbol	Pearson symbol letters
Triclinic	P	aP
Monoclinic	P	mP
	C	mC
Orthorhombic	P	oP
	C	oC
	F	oF
	I	oI
Tetragonal	P	tP
	I	tI
Hexagonal (and trigonal P)	P	hP
Rhombohedral	R	hR
Cubic	P	cP
	F	cF
	I	cI

Pearson symbol and space group

The Pearson symbol does not uniquely identify the space group

Space group

In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...

of a crystal structure, for example both the NaCl structure, (space group Fmm) and diamond (space group Fdm) have the same Pearson symbol cF8.