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A filled square marking a fourfold axis.
Also known as: Tetrad axis symbol, Four-fold axis mark, Square symmetry symbol
The graphical symbol for a fourfold rotation axis on a crystallographic space group diagram, drawn as a solid square.
Marks a fourfold rotation axis, an axis about which the structure repeats after a quarter turn.
Contexts: Laboratory
Cannot occur in a molecule of arbitrary shape but can in a crystal, because a lattice only permits axes of order two, three, four and six.
Contexts: Laboratory
A small solid square standing on one corner, its four points marking the order of the axis.