Specific terms are used to describe the texture of igneous rocks. If an igneous rock is composed of grains larger than 1 cm it is considered to have a pegmatitic texture . Those with grain sizes ranging from 1 to 10 mm, have a phaneritic texture . Rocks with an aphanitic texture have grains less than 1 mm in diameter. If a rock is composed entirely of volcanic glass it has a hyaline texture .
Some igneous rocks have more than one distinct grain size.
Rocks such as this have a porphyritic texture . The large grains in a porphyry are referred to as phenocrysts . These textural terms are reserved strictly for igneous rocks. Other textural terms used for igneous rocks shown in outline form below. Igneous rocks are classified using texture and composition.