In igneous and metamorphic rocks, a mineral takes this form when it crystallizes late from a magma or fluid, forced to fill the irregular gaps left by earlier-forming crystals. Because its shape is dictated entirely by its surroundings rather than its internal atomic structure, it shows no flat geometric crystal faces. Petrologists use these textures to determine the exact sequence in which a rock solidified.
Heard on the job
The thin section shows large euhedral plagioclase laths surrounded by xenomorphic quartz filling the interstitial spaces.
Insider tip
The prefix xeno means foreign or strange, reminding geologists that the mineral's shape is imposed by outside forces rather than its own crystal habit.
Also heard as
- anhedral
- allotriomorphic