Porphyritic rocks

variety of igneous rock

Basanite () is an igneous, volcanic (extrusive) rock with aphanitic to porphyritic texture. It is composed mostly of feldspathoids, pyroxenes, olivine, and calcic plagioclase and forms from magma low in silica and enriched in alkali metal oxides that solidifies rapidly close to the Earth's surface.

thumb|Minette (a type of lamprophyre), from Jáchymov in the Czech Republic

thumb|upright=1.3|Cross-polarized light microscope image of an intergrowth of quartz and alkali feldspar in a granophyre (Muskox intrusion), as seen in [[thin section (Long dimension is 1.5 mm)]] Granophyre ( ; from granite and porphyry) is a subvolcanic rock that contains quartz and alkali feldspar in characteristic angular intergrowths such as those in the accompanying image.

thumb|Porphyritic texture in a granite. This is an Intrusive rock|intrusive porphyritic rock. The white, square feldspar [[phenocrysts are much larger than crystals in the surrounding matrix; eastern Sierra Nevada, Rock Creek Canyon, California.]] thumb|A porphyritic volcanic sand grain, as seen under the petrographic microscope. The large grain in the middle is of a much different size class than the small needle-like crystals around it. Scale box in millimeters. Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, w

Roman-period Egyptian porphyry quarry

thumb | right | Ankaramite lava flow Ankaramite is volcanic rock type of mafic composition. It is a dark porphyritic variety of basanite containing abundant pyroxene and olivine phenocrysts. It contains minor amounts of plagioclase and accessory biotite, apatite, and iron oxides.

thumb|Quartz porphyry from the island of Alnön|Alnö, Sweden. [[Phenocrysts of clear glassy rounded quartz and white orthoclase feldspar are set in a fine-grained matrix. Sample is just over 10 cm long]] Quartz-porphyry, in layman's terms, is a type of volcanic (igneous) rock containing large porphyritic crystals of quartz. These rocks are classified as hemi-crystalline acid rocks.