Crystal Lab › The 230 space groups › Orthorhombic
No. 51 P m m a
Orthorhombic space group · 8 symmetry operations per cell · 12 Wyckoff positions · 6 settings
Symmetry elements and Wyckoff positions (interactive)
No. 51 P m m a
SettingLoading the group…
x = 0.10, y = 0.17, z = 0.08
- Number
- 51
- Hermann–Mauguin symbol
- P m m a
- Hall symbol
-P 2a 2a- Crystal system
- Orthorhombic
- Operations per cell
- 8
- General position
- 8l (site symmetry 1)
Wyckoff positions (standard setting)
| Multiplicity | Letter | Site symmetry |
|---|---|---|
| 8 | l | 1 |
| 4 | k | m.. |
| 4 | j | .m. |
| 4 | i | .m. |
| 4 | h | .2. |
| 4 | g | .2. |
| 2 | f | mm2 |
| 2 | e | mm2 |
| 2 | d | .2/m. |
| 2 | c | .2/m. |
| 2 | b | .2/m. |
| 2 | a | .2/m. |
How to read it
- Each symmetry element drawn in the cell is worked out from the group’s operations: rotation and screw axes as lines (arrow = direction; dashed = screw), mirror and glide planes as sheets (dashed outline = glide), inversion centres as dots; rotoinversion axes are dotted. Colours: 2-fold red, 3-fold green, 4-fold blue, 6-fold purple.
- The multiplicity is how many equivalent points an atom on that site generates in the conventional cell; the general position has the highest multiplicity, equal to the number of operations.
- Site symmetry is the point group that leaves that position fixed; a special position (lower multiplicity) sits on a symmetry element — press + on a row to see its atoms land on the drawn elements.