Science, Tech, Math › Science The Textures of Igneous Rocks Share Flipboard Email Print Marco Bottigelli / Getty Images Science Geology Types Of Rocks Landforms and Geologic Features Geologic Processes Plate Tectonics Chemistry Biology Physics Astronomy Weather & Climate By Andrew Alden Geology Expert B.A., Earth Sciences, University of New Hampshire Andrew Alden is a geologist based in Oakland, California. He works as a research guide for the U.S. Geological Survey. our editorial process Andrew Alden Updated November 05, 2019 The texture of a rock refers to the details of its visible character. This includes the size and quality and interrelations of its grains and the fabric they form. Larger scale features, such as fractures and layering, are considered rock structures in comparison. There are nine main types of igneous rock textures: Phaneritic, vesicular, aphanitic, porphyritic, poikilitic, glassy, pyroclastic, equigranular, and spinifex. Each kind of texture has a variety of different characteristics that make them unique. Properties of Igneous Rock Textures What determines igneous rock texture? It all comes down to the rate at which the rock cools. Other factors include the diffusion rate, which is how atoms and molecules move through the liquid. The rate of crystal growth is another factor, and that's how quickly new constituents come to the surface of the growing crystal. New crystal nucleation rates, which is how enough chemical components can come together without dissolving, is another factor affecting the texture. Texture is comprised of grains, and there are a few main types of igneous rock grains: Equant grains are those with boundaries of equal lengths; rectangular tablet shapes are known as tabular grains; acicular grains are slender crystals; long fibers are known as fibrous grains, and a grain that is prismatic is one that has different types of prisms. 01 of 09 Aphanitic Texture James St. John/Flickr Aphanitic ("AY-fa-NIT-ic") rocks have mineral grains that are mostly too small to be seen with the naked eye or a hand lens, like this rhyolite. Basalt is another igneous rock with the aphanitic texture. 02 of 09 Equigranular Texture James St. John/Flickr Rocks with equigranular ("EC-wi-GRAN-ular") have mineral grains that are generally the same size. This example is a granite. 03 of 09 Glassy Texture Michael Szönyi / Getty Images Glassy (or hyaline or vitreous) rocks have no or almost no grains at all, as in this quickly chilled pahoehoe basalt or in obsidian. Pumice is another type of igneous rock with a glassy texture. 04 of 09 Phaneritic Texture James St. John/Getty Images Phaneritic ("FAN-a-RIT-ic") rocks have mineral grains that are large enough to be seen with the naked eye or a hand lens, like this granite. 05 of 09 Poikilitic Texture James St. John/Getty Images Poikilitic ("POIK-i-LIT-ic") texture is one in which large crystals, like this feldspar grain, contain small grains of other minerals scattered inside them. 06 of 09 Porphyritic Texture Dorling Kindersley / Getty Images Rocks with porphyritic ("POR-fi-RIT-ic") texture like this andesite have larger mineral grains, or phenocrysts ("FEEN-o-crists"), in a matrix of smaller grains. In other words, they display two distinctive sizes of grains that are visible to the naked eye. 07 of 09 Pyroclastic Texture Mangiwau / Getty Images Rocks with pyroclastic ("PY-ro-CLAS-tic") texture are made of pieces of volcanic material that are created in an explosive eruption, like this welded tuff. 08 of 09 Spinifex Texture James St. John/Flickr Spinifex texture, found only in komatiite, consists of large crisscrossing platy crystals of olivine. Spinifex is a spiny Australian grass. 09 of 09 Vesicular Texture James St. John/Flickr Rocks with vesicular ("ve-SIC-ular") texture are full of bubbles. It always indicates a volcanic rock, like this scoria.