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The six main types of textures are phaneritic, aphanitic, porphyritic, glassy, pyroclastic, and pegmatitic. Aphanitic (a = not, phaner = visible) rocks, in contrast to phaneritic rocks, typically form from lava which crystallize rapidly on or near Earth's surface.
In geology, texture or rock microstructure [1] refers to the relationship between the materials of which a rock is composed. [2] The broadest textural classes are crystalline (in which the components are intergrown and interlocking crystals), fragmental (in which there is an accumulation of fragments by some physical process), aphanitic (in which crystals are not visible to the unaided eye ...
Porphyritic texture in a granite. This is an intrusive porphyritic rock. The white, square feldspar phenocrysts are much larger than crystals in the surrounding matrix; eastern Sierra Nevada, Rock Creek Canyon, California. A porphyritic volcanic sand grain, as seen under the petrographic microscope. The large grain in the middle is of a much ...
USGS scientist examines pumice blocks at the edge of a pyroclastic flow from Mount St. Helens Rocks from the Bishop Tuff, uncompressed with pumice on left; compressed with fiamme on right. Flight through a μCT-image stack of a lapillus of the volcano Katla in Iceland. Find spot: Beach near Vik at the end of road 215. Acquisition done using "CT ...
The lithology of this porphyritic basalt is characterized by olivine and augite phenocrysts. The texture of a rock describes the relationship between the individual grains or clasts that make up the rock. Sedimentary textures include the degree of sorting, grading, shape and roundness of the clasts. [22]
"Imperial Porphyry" from the Red Sea Mountains of Egypt A waterworn cobble of porphyry Rhyolite porphyry from Colorado; scale bar in lower left is 1 cm (0.39 in). Porphyry (/ ˈ p ɔːr f ə r i / POR-fə-ree) is any of various granites or igneous rocks with coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate-rich, generally aphanitic matrix or groundmass.
Graph of komatiite geochemistry MgO% vs Cr ppm, from basal flows, Wannaway, Western Australia. The pristine volcanic mineralogy of komatiites is composed of forsteritic olivine (Fo90 and upwards), calcic and often chromian pyroxene, anorthite (An85 and upwards) and chromite.
Andesite is an aphanitic (fine-grained) to porphyritic (coarse-grained) igneous rock that is intermediate in its content of silica and low in alkali metals. It has less than 20% quartz and 10% feldspathoid by volume, with at least 65% of the feldspar in the rock consisting of plagioclase.