microgranular

Microgranular is an adjective that describes a material composed of very small grains or crystals. The term is used in geology, petrology, and materials science to characterize textures and microstructures where individual grains are too small to be seen with the naked eye.

In geology, microgranular texture refers to igneous rocks whose groundmass is fine-grained and interlocking, with crystals too small to be discerned without magnification. This texture often indicates rapid cooling or crystallization in a restricted volume and yields a uniform, glassy-to-fine appearance. While the descriptor is common in petrographic descriptions, it does not itself define a mineralogical class; rocks with microgranular textures may be described as microgranular basalts, microgranular diorites, or simply fine-grained varieties depending on mineral content.

In materials science, microgranular describes a polycrystalline or fine-grained microstructure in which constituent grains are sub-millimeter in size. Here, microgranularity can influence mechanical properties such as strength, hardness, and toughness and is often examined by optical microscopy or scanning electron microscopy. The term is often used interchangeably with microcrystalline or fine-grained, though some sources distinguish microgranular from strictly glassy or amorphous textures.

See also microcrystalline, fine-grained, polycrystalline.