twinning: Quick Facts

Written and fact-checked by

The Information Architects of Encyclopaedia Britannica

Photos

Diagram showing several shapes of natural calcite crystals. The top section illustrates four untwinned crystal habits, each with different geometric forms. The bottom section displays two examples of twinned calcite crystals, highlighting how their structures differ. Red dashed lines and axes indicate symmetry and orientation.

Relations between lamellar twinning and cleavage planes in dolomite and calcite. This difference can be discerned best when thin sections of the minerals are viewed under a microscope.

Figure 2: Twinning in feldspars.

See All Images →

Topics

albite twin twin plane twin centre twin axis penetration twin grid twinning Carlsbad twin crystal deformation and flow slip radiation damage liquid crystal pleochroism double refraction strain symmetry polymorphism Brewster’s law How are crystals made?