This petrographic term describes an igneous or metamorphic rock where the grains show a slight but noticeable variation in dimension. It falls between a perfectly uniform equigranular texture and a distinctly porphyritic one where large crystals stand out against a fine matrix. Geologists use this texture to interpret cooling rates, indicating a mostly steady crystallization process with minor fluctuations.
Heard on the job
Under the hand lens, the granite appears subequigranular with just a few slightly larger feldspar phenocrysts.
Do not mix it up with
- Equigranular: Equigranular means all crystals are practically identical in size, while subequigranular allows for a slight, visible variation.