Basalt is a common extrusive igneous (volcanic) rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon. Flood basalt describes the formation in a series of lava basaltflows.
Basaltis defined by its mineral content and texture, and physical descriptions withoutmineralogical context may be unreliable in some circumstances. Basalt isusually grey to black in colour, but rapidly weathers to brown or rust-red dueto oxidation of its mafic (iron-rich)minerals into hematite andother iron oxides and hydroxides. Although usually characterized as"dark", basaltic rocks exhibit a wide range of shading due toregional geochemical processes.
Uses: Basalt is used inconstruction (e.g. as building blocks or in the groundwork), making cobblestones (fromcolumnar basalt) and in making statues.Heating and extruding basalt yields stone wool,said to be an excellent thermal insulator.
Andesite is an extrusive igneous, volcanic rock, of intermediatecomposition, with aphanitic to porphyritic texture. In a general sense, it is the intermediatetype between basalt and granite, and ranges from 57 to 63% silicon dioxide (SiO2) as illustrated in TAS diagrams. The mineralassemblage is typically dominated by plagioclase plus pyroxene or hornblende. Magnetite, zircon, apatite, ilmenite, biotite, and garnet are common accessory minerals. Alkali feldspar may be present in minor amounts. The quartz-feldspar abundances in andesite and other volcanic rocks are illustratedin QAPF diagrams.
LavaStone (Volcanic rock, often shortened to volcanics in scientificcontexts) is a rock formed from magma erupted froma volcano. In other words,it differs from other igneous rock by being of volcanic origin. Likeall rock types, the concept of volcanic rock is artificial, and in naturevolcanic rocks grade into hypabyssal and metamorphic rocks andconstitute an important element of some sediments and sedimentary rocks. For thesereasons, in geology, volcanics and shallow hypabyssal rocks are not alwaystreated as distinct. In the context of Precambrian shield geology, the term "volcanic" is often appliedto what are strictly metavolcanic rocks.
Porphyry is a textural term for an igneous rock consisting of large-grained crystals such as feldspar or quartz dispersed ina fine-grained silicate rich,generally aphanitic matrix or groundmass. The larger crystals are called phenocrysts. In itsnon-geologic, traditional use, the term porphyry refers to the purple-red form of this stone, valued forits appearance.
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