Volcanic rock, also called Effusive rock, belongs toMagmatic rock(igneous rocks)MagmaIt is the extrusive rock formed by condensation after being ejected to the surface through the crater.Volcanic rock refers to magma erupting from the surfaceAtmosphereandHydrosphereIt is formed by moderate cooling crystallization. When the magma erupts along the fissure, the volcanic rock shape is generally in harmony with the surface shape, in the form of quilt or layer.[1]
Chinese name
lava
Foreign name
Volcanic Rock
Structure
Aphanitic, semi crystalline, glassy and other structures
Volcanic rock refers to the rock formed by the hot magma from the deep part of the earth ejected to the surface through the crater and condensed. It can be divided into volcanic rock in the narrow sense and volcanic rock in the broad sense.
Volcanic rocks in a narrow sense refer to volcanic lava, which is some magma with low viscosity and low volatile matter (such as basic magma) flowing out of the volcanic crater in the form of melt. Some high viscosity acidic magma can also form lava in the late stage of volcanic eruption when a large amount of volatile matter in the magma chamber escapes from the surface after escaping.
The composition of magma is different, and the rocks formed after cooling and solidification are also different.The basic extrusive rock isbasalt, neutral extrusive rock isAndesite, acidic extrusive rock isRhyolite, semi alkaline and alkaline extrusive rocks areTrachyteandPhonolite。
In a broad sense, volcanic rocks includeVolcaniclastic rock。Pyroclastic rocks are mainly acidic rocks with high viscosity and high volatile content that will erupt to the surface in an explosive manner, often mixed with a certain amount of normal sediment or lava materials.[2]
Volcanic lava is some magma with low viscosity and low volatile matter (such as basic magma) flowing out of the volcano crater in the form of melt. Some acid magma with high viscosity intrudes out of the surface after a large amount of volatile matter escapes from the magma chamber in the late stage of volcanic eruption, and can also form lava.
According to the different magma composition, volcanic lava can be divided into the following different types of volcanic lava.[3]
Ultramafic lava
The ultramafic volcanic lava mainly includes picrite, Mameji rock and Komatite rock.
Picrite is often formed in continental overflow basalt area or oceanic overflow basalt area related to mantle plume activity, such as China'sMount EmeiBasalt Province.A small amount of picrite is also formed in an island arc environment related to subduction, such as the Kamnoops area in Great Britain, Canada.
Mameji rock：It is also called glassy dunite.The rock has a glassy porphyritic structure, olivine is phenocryst, and the matrix is blackVolcanic glass, sometimes containing a small amount of titaniumAugiteMicrocrystal.
Komatite：It often occurs as rock flow or hypabyssal rock mass.The rock consists of olivine, pyroxene and a small amount ofMetallic mineralsAnd basic glass.Common pillow structure with uniqueSpiny structure。
basalt：It is mainly composed of augite, basic plagioclase and volcanic glass.Stomatal structure and almond structure are developed, which are mainly porphyritic and non porphyritic cryptocrystalline structures, and the matrix is mostly microcrystalline cryptocrystalline.According to the tectonic background of its occurrence, it can be divided into different types: such as mid ocean ridge basalt, ocean island basalt, continental overflow basalt, continental rift basalt, and basalt related to subduction zone.
Neutral volcanic lava
According to QAP diagram, neutral volcanic lava can be divided intoAndesite、Andesite、Trachyte, alkali feldspar trachyte and quartz andesiteQuartz trachyteQuartz alkali feldspar trachyte.
Andesite：It often has a porphyritic structure, and the phenocrysts are mostly dark minerals such as medium feldspar and pyroxene, hornblende, biotite, etc. The phenocrysts of hornblende and biotite often have melting and darkening edges.The matrix is mainly composed of medium feldspar.
Volcaniclastic rock
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Volcaniclastic rock
Pyroclastic rocks are rocks formed by diagenesis after various kinds of debris produced by explosive volcanic activities are accumulated through air or water media.In terms of rock composition, it has the characteristics of igneous rocks similar to volcanic lava, but in terms of structure and structure, it has the characteristics of some igneous rocks as well as some sedimentary rocks.
According to the classification method of Sun Shanping (2001), volcaniclastic rocks are divided into normal volcaniclastic rocks, volcaniclastic rocks transiting to lava and volcaniclastic rocks transiting to sedimentary rocks.[4]
Normal pyroclastic rocks
Volcanic debris volume fraction is more than 90%, and normal sediment and lava materials are very few.According to diagenesis mode and structural characteristics, it can be divided intocommon pyroclastic rack 、welded volcaniclastic rock And 3 subtypes of stratovolcaniclastic rocks.
Ordinary pyroclastic rock subclass：The diagenetic mode is mainly compaction, often superimposed with hydrochemical cementation.Pyroclastic materials are mainly composed of volcanic agglomerations, volcanic breccia, volcanic gravel, crystal chips and semi plastic glass chips. They are mainly rigid and semi plastic chips, and there is no plastic deformation such as flattening and stretching after accumulation.It can be divided intoAgglomerate、Volcanic breccia, volcanic breccia and tuff.
Fusion volcaniclastic rock subclass:Pyroclastic materials still have high temperature after accumulation and are in a plastic state. They are formed by deformation and melting under the load pressure of overlying materials.The rock has fusion structure, and the debris is mainly composed ofCrystal chip, plastic rock debrisPlastic shavingsandVolcanic dustIt can also have a small amount of rigiditydebris, due to plastic deformation debris stretching and orientationFlow structure。
According to the particle size of the debris, it can be divided into agglomerate, breccia andFused tuff。
Stratum volcaniclastic rock subclass:It refers to volcaniclastic rocks with obvious rhythmic bedding and bedding structure, and layered tuff is more common.
Layered tuff is generally formed by the accumulation of volcanic ash in a water basin, in which the volume fraction of normal sediment is less than 10%. Pyroclastic materials are mainly glass debris, rigid semi plastic rock debris and volcanic dust, which are cemented by a small amount of hydrochemical sediment decomposed by volcanic ash and volcanic dust, and some are compacted.When the volume fraction of normal sediment is greater than 10%, it will transition toSedimentary tuff。
Pyroclastic rocks transiting to lava
Volcanic clasts account for 10% - 90% in volume, and the clasts are cemented by molten slurry, which can be called volcaniclastic lava.
The genesis of clastic lava is diverse:
1. When the lower molten slurry continues to flow and the escaping gas explodes, the solidified lava crust will be broken and cemented by lava to form breccia lava and agglomerated lava;
2. When the eruption energy is insufficient, the debris is often thrown out of the crater, and at the same time, the lava overflows, and the debris falling into the lava is cemented by the lava to form various clastic lava;
3. When the lava is ejected from the volcano crater with a greater impact, most of the phenocrysts in the lava can be broken, forming a crystal chip tuff lava with crystal chips as the main debris;
4. The cryptoexplosion of magma in the underground often causes the internal phenocrysts to be broken and crystal tuff lava can also be formed.
Pyroclastic rocks transiting to sedimentary rocks
It is formed by the accumulation of pyroclastic rocks falling into the basin and normal sediments at the same time.According to the content of pyroclastic materials, it can be divided into sedimentary pyroclastic rocks and pyroclastic sedimentary rocks.
Sedimentary volcaniclastic rock subclass:Volcanic clasts account for 50% - 90% of the total volume, often associated with normal volcaniclastic rocks and normal sedimentary rocks, and often in a transitional relationship.
According to the grain size of volcanic debris, it can be divided into sedimentary block rock, sedimentary volcanic breccia andSedimentary tuffSedimentary tuff is common.The rock has bedding structure, and the rhythmic layer is relatively developed.Normal sediments such as rounded gravel, sand and clay are commonly found in debris, and sometimesBiofossilAnd bioclasts.
Volcanic clastic sedimentary rock subclass:Volcanic clasts have a small volume fraction, between 10% and 50%, and are more similar to sedimentary rocks. They often have a gradual transition relationship with sedimentary volcaniclastic rocks. The accumulation location is generally far from the crater. When naming, the name of normal sedimentary rocks is taken as the basic name, and the volcaniclastic rocks are prefixed, such asTuffaceous sandstone、tuffaceous conglomerate Etc.
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And othersNatural stoneIn contrast, volcanic rock has superior performance. In addition to the general characteristics of ordinary stone, it also has its own unique style and special functions.Take basalt as an example. Compared with marble and other stones, basalt stone has low radioactivity, which makes it safe to use in human living places, and will not make consumers who choose stone for interior decoration uncomfortable.
Volcanic rock is hard and can be used to produce ultra-thin stone plates. After surface polishing, the glossiness can reach more than 85 degrees. The color is bright and pure, and the appearance is elegant and solemn. It is widely used for various building exterior wall decoration and the ground pavement of municipal roads, squares, and residential quarters. It is also the preferred stone for various antique buildings, European buildings, and garden buildings,It is deeply loved and welcomed by customers at home and abroad.
Volcanic rock material is weather resistant, weather resistant and durable;Sound absorption and noise reduction are conducive to improving the auditory environment;Simple and natural to avoid glare, which is beneficial to improving the visual environment;Water absorption, skid resistance and heat resistance are beneficial to improving the physical environment: the unique "breathing" function can adjust the air humidity and improve the ecological environment.All kinds of unique advantages can meet the needs of people in today's era to pursue the new fashion of simple nature and green environmental protection in building decoration.
Volcanic rock cast stone pipes have wear resistance and corrosion resistance.It can replace harmful asbestos and glass products and metal materials without losing the advantages of glass, metal and other materials.Compared with metal, it has light weight, corrosion resistance and long service life.The service life of volcanic rock cast stone pipe can reach 100 years, and its elasticity and toughness are much higher than those of steel.
In addition, the plasticity of volcanic rock cast stone bar is higher than that of plastic, its plate strength is higher than that of light metal alloy, it can withstand the rolling of tanks, and its corrosion resistance is far higher than that of glass.Some scientists have certified this.
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Hong Kong
Hexagonal columnar volcanic rock
Guozhou Islands, there is a famous hexagonal columnar volcanic rock in North Guozhou.Volcanic rocks composed of black basic basalt are also abundant around the world, but large area hexagonal columnar jointed volcanic rocks cooled by flesh red acidic rhyolitic volcanic rocks are rare in the world.The volcanic rocks here are arranged into huge hexagonal stone columns, and an island called Pebble Row opens to the east, which is more eye-catching
The unique stone column array of Jiedakai: numerous stone columns are arranged in the center of the island level by level, forming a natural spiral stone ladder, which is a spectacle.
Guangxi
Weizhou Island, Volcano Crater Geopark is famous for its spectacular volcanic lava.On January 13, 2010, it successfully passed the review and assessment of the expert review team of the National Tourism Administration, and was rated as a national 4A tourist attraction by the National Tourism Administration.
