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Identification characteristics of common magmatic rocks

Release date:2018-12-21  source:中南选矿网  Browse times:134
Core Tips: I. Requirements of the experiment: Through experiments, understand and basically grasp the macroscopic identification and description methods of magmatic rocks, and master the mineral composition, structural and structural characteristics of the magmatic rocks and the main rock types.

I. Requirements of the experiment: Through experiments, understand and fundamentally grasp the macroscopic identification and description methods of magmatic rocks, and master the mineral composition, structural and structural characteristics of the magmatic rocks and the identification characteristics of major rock types. II. Experimental contents and methods: Ultrabasic rocks: peridotite, pyroxenite, amphibolite, kimberlite basic rock: gabbro, diabase, basalt neutral rock: diorite, andesite, positive length Rocks, coarse porphyry acid rocks: granite, rhyolite dykes: the main identification characteristics of magmatic rocks listed in the textbooks of lamprophyre and fine-grained rocks. Under the naked eye, the main types of rock types are observed by means of magnifying glasses and knives. Mineral composition, structural structure and other characteristics. III. Identification method and steps of magmatic rock limit The observation of magma rock hand specimens is generally to observe the color, structure, structure, mineral composition and content of the rock, and finally determine the rock name. 1) Color: It mainly describes the color of the fresh surface of the rock, and also pay attention to the color after the weathering. Directly describe the overall color of the rock, such as purple, green, red, brown, gray and other colors. If some colors are somewhere in between, use compound names such as off-white, yellow-green, and magenta. The color of the magmatic rock is reflected in the relative content of dark minerals and light minerals. A ship with a dark mineral content >60% is called dark rock; 60-30% is called medium color rock; <30% is called light color rock. 2) Structure: According to the degree of crystallization of each component in the rock, it can be divided into all-crystalline, semi-crystalline, vitreous and other structures. Descriptive content and method of magmatic rock structure: Full crystalline crystalline coarse grain: >5mm; medium grain: 1~5mm; fine grain: <lmm; Describe the particle size, morphology and shape of the total mineral and different minerals The content of unequal granules: describes the size and content of the largest, smallest and intermediate size particles like plaque structure: large is phenocryst, small is matrix. Describe the relative content of plaque matrix, composition, shape, size, cryptocrystalline description color, fracture characteristics, semi-crystalline plaque structure (vitreous + crystalline): describe phenocryst composition, shape, size and content; matrix part Content, color, fracture characteristics Glassy description color, fracture characteristics 3) Structure: Intrusive rocks are often block-like structures, minerals in rocks are not oriented; sprayed rocks often have stomatal, almond-like and rhyolite structures. Pay attention to the size and shape of the stomata, the filling of the almonds, the stomata, and the orientation of the almonds. 4) Mineral composition: Mineral composition and its content are important basis for the naming of magmatic rocks. All minerals in the rock that can be identified with the naked eye are described. First, the composition, shape, size, physical properties and relative content of the main minerals should be described. Secondly, the secondary minerals should also be briefly described. 5) Secondary changes: After the consolidation of magmatic rocks, the hydrothermal action and surface weathering of the magma period often cause all or part of the minerals in the rock to undergo secondary changes. If the change is strong, it should be described as etched. What kind of minerals. Such as olive stone, pyroxene easy to form serpentine, hornblende, biotite often become chlorite, while feldspar becomes sericite, kaolinite and so on. 6) Rock name: The rock name is determined based on the observation and description of the meat limit. Color + structure + basic rock name, such as light gray coarse grain granite; grey black medium grain gabbro magmatic rock classification, beginners can be carried out according to the following steps: (1) view color, initial class: rock color reflection The mineral composition and its content are the direct basis for rock classification and naming. However, it should be pointed out that when estimating the dark mineral content, it is easy to cause visual errors. When light-colored minerals are coated on dark minerals, due to its transparency, it is easy to regard it as a dark mineral, so the estimation of dark mineral content is often high. Also pay attention to the influence of the color of the secondary changes. (2) Demonstration of minerals: according to the color is divided into three parts, according to the mineral species, content and symbiotic combination characteristics, the rock is divided into (1) ultrabasic rocks, (2) basic rocks, (3) Neutral (calcium-alkaline) rock, (4) acid rock, (5) alkaline rock, etc., can determine which type of rock belongs to. Method: Indicating that the mineral is divided into two ends, the dark minerals are in the middle, and the symbiotic minerals are tested. Quartz>20% is acid rock; olivine (+ pyroxene, or amphibole)>90% is ultrabasic rock; medium and basic rocks are all plagioclase + color dark mineral; medium and basic rock In addition to the color removal rate, there are two main rules: 1 dark mineral species: neutral rocks are mainly hornblende, basic rocks are mainly pyroxene; 2 symbiotic minerals: basic rocks and ultrabasic rocks A small amount of olivine can be found; the neutral rock is adjacent to the acid rock, and a small amount of quartz and meat red potassium feldspar can be found. The color of acid rock and alkaline rock are near flesh red, and the distinction between the two is mainly based on the fact that the content of quartz and plagioclase (off-white) in alkaline rock is very small. For the effusion rock and the diagenetic rock with porphyry structure, the matrix is ​​cryptocrystalline, and it is difficult for the naked eye to identify its constituents, which are mainly named by phenocrysts. Because plaques are generally composed of the main minerals in the rock, plaque minerals can also be named. For plaque-free cryptocrystalline rocks, it is only roughly judged by the color of the rock and the degree of compactness. Acidic cryptocrystalline rocks with higher SiO2 tend to have greater hardness. (3) Look at the structure (structure), push the environment (production): the same rock composition is the same, but each type is divided into three types: deep diagenesis, superficial diagenesis and effusion rock according to different occurrences, giving different rock species names. The rock occurrence is the rock formation environment, which is mainly reflected in the structure and structure. There are many types of rocks in nature, and there are many types of transitions between categories. For example, a rock is dominated by hornblende and plagioclase, and secondary minerals are quartz (up to 5-20%), potassium feldspar (up to 20%), biotite, etc., and the rock should be between medium and acidic. It is designated as granodiorite; some is between the eruptive rock and the shallow diagenesis, which is called ultra-shallow diagenesis. (4) According to the color of the rock, the main, minor mineral content and structural structure, the name is detailed. For intrusive rocks: color + structure + basic name such as: black gray medium grain gabbro for ejected rock: color + structure + basic name such as: black stomatal basalt magmatic rock system classification table: 2, magma rock meat identification Description: The sample n is dark gray, the weathered surface is slightly blackish green, and the grain structure is equal. The particles are generally in the shape of l 1.5 mm. The main minerals are plagioclase and pyroxene, each accounting for 55%. 40% or so. The plagioclase is grayish white, columnar or granular. When the cleavage surface is sparkling, the glass is shiny, the pyroxene is black, short columnar, glass luster, and some cleavage surfaces are clear. The rocks are fresher and the last time they change. According to the various characteristics of the n-type specimen rock described above, it can be defined as basic and deep diagenesis, and it is named: black-gray medium-gypsum gabbro. 4. Operation 1. Compare the main differences between the following two types of magmatic rocks: gabbro and diorite; basalt and andesite; andesite and rhyolite; granite and syenite 2. The magma sample designated by the teacher is required. Identification. Identification characteristics of common sedimentary rocks in Experiment 8 (3 hours) "Experimental requirements: Through experiments, understanding and basic understanding of the naked eye identification and description methods of sedimentary rocks, understanding the mineral composition, structure, bedding, stratigraphic characteristics and major rock types of sedimentary rocks Identification characteristics. II. Experimental content and methods: Clastic rocks: conglomerate, sandstone, siltstone clay rock: shale, mudstone chemical rock and biochemical rock: carbonate rock: limestone, marl, dolomite; silicon Protozoic rocks; volcanic clastic rocks such as ferritic rocks: the main identification features of sedimentary rocks listed in the volcanic breccia and tuff control textbooks. The main mineral components and structural and structural features of different rock types are observed under the naked eye by means of magnifying glasses and knives. Sedimentary rocks are formed by diagenesis of sediments formed by external dynamic geological processes. The characteristics of sedimentary rocks are mainly recognized by their color, structure, structure and composition, and sedimentary rocks are generally layered. According to genesis and composition, they can be roughly classified into: 1. Clastic rocks: including normal clastic rocks, pyroclastic rocks; 2. Chemical rock and biochemistry Rock. I) The color of sedimentary rocks: The color of sedimentary rocks often reflects the composition and environment of the rocks. The white sedimentary rocks are mostly composed of pure kaolin, quartz, calcite and salt. Dark gray-black generally indicates that the rocks contain organic matter. Impurities such as iron sulfide or slag, which are formed in a reducing environment; flesh red or deep red may contain more feldspar or iron oxide, which is formed in an oxidizing environment; silicic acid containing ferrous iron The salt forms a green sedimentary rock, which is formed in a weakly reducing environment. The system classification table of sedimentary rocks: 2) The structure of sedimentary rocks: The bedding and layer structures are peculiar structures of sedimentary rocks. The sedimentary rocks show their non-uniformity due to the bedding structure, and the bedding is: horizontal The undulating, sloping, staggered, etc., can not see the layered bedding of the bedding structure. The layer structure is the trace left by various geological processes on the surface of the sediment. Commonly there are wave marks and mud. Cracks, rain marks, insects, etc. III) Sedimentary rock structure: The structure of sedimentary rocks is closely related to the genesis of sedimentary rocks: clastic rocks with clastic knots The chemical structure has chemical structure and biological structure. Debris structure: According to the diameter of the debris particles, it can be divided into: Gravel structure: >2mm Sand structure: 0.05-2mm silty structure: 0.O05—0.05mm. Mud structure: <0.005mm. Chemical structure: Mineral is a structure formed by chemical precipitation in a colloidal solution or a true solution. It can be cryptocrystalline or crystallized. Biological structure: almost all or most of the rock is composed of biological remains (such as shells). IV. Mineral composition of sedimentary rocks: There are more than 20 kinds of common minerals in sedimentary rocks, and the mineral composition in various sedimentary rocks is more Large difference. Clastic rock consists of two parts: detrital particles (rock debris and mineral debris) and cement. Detrital minerals are mainly quartz, feldspar and muscovite, which are not easily weathered, and easily weathered olivine and pyroxene. Amphibole is rare. Common cements are carbonate, silica, iron oxide, mud and so on. According to the hardness of silicon, the mud is soft, the calcium is diluted with dilute hydrochloric acid, and the iron is reddish brown (ferric iron) or grayish green (divalent iron), which can distinguish the above four cements. . Chemical and biological rocks have many mineral components, such as iron, aluminum, manganese, silicon oxides and hydrogen itch compounds, carbonates (calcite and dolomite), sulfates (gypsum, etc.), phosphates, halides, etc. . However, the composition of a certain type of rock is relatively simple, and it is often dominated by a certain chemical component. Third, the identification method and steps of the sedimentary rock: 1. Clastic rock: has a typical debris structure, observe and describe the following: 1) Color: It is required to indicate the overall color of the rock, and to distinguish the color of the fresh surface and the weathered surface. 2) Construction: See if there are micro-layered and layered structures, which are generally common in block structures. 3) Structure: Clastic rock has a typical detrital structure and consists of two parts: 1. Debris part: Describes the size and content of clastic particles. If it is coarse clastic rock, it describes the size and shape of gravel or breccia. , roundness and so on. 2, cemented parts: common cements are: clay: soil, the rock is loose, the knife can be infused, and can be soaked in water. Iron: Makes the rock purple or brown. Siliceous: white, harder than a knife, often tightly bonded. Calcium: White with dilute hydrochloric acid strongly foaming. 4) Debris composition: common: quartz, feldspar, muscovite and cuttings, determine the composition and content of debris. 5) Nomenclature: The clastic rock is firstly determined according to the size of the clastic particles: conglomerate, sandstone, siltstone, argillaceous rock, basic name, and then subdivided according to the crumb size and composition. 2. Mudstone: The argillaceous rock is composed of clay minerals. The mineral particles are very small, so it is difficult to visually identify the components in hand specimens. The main observations describe the color and physical properties of argillaceous rocks. 1) Color: The general argillaceous rock is often light, and the mixed organic matter is black. The iron oxide mixed with brown is brown, and the chlorite and glauconite are green. 2) Physical properties: Observe the fracture, hardness and plasticity of the rock face, whether it is easy to soften in water, and the water absorption is strong. 3) Structure: Observe the presence or absence of bedding, wave marks, tuberculosis, mud cracks, etc. in the rock. 4) Whether it contains biological fossils. 5) The argillaceous rock is easily confused with the siltstone: the meat limit is generally identified by grinding the rock powder by hand, and whether there is a sand sensation to distinguish it. If there is no sand sensation, it is designated as argillaceous rock. 6) Naming: The further classification of argillaceous rock itself is divided into clay, mudstone and shale according to the degree of consolidation and the presence or absence of phylogenetic structure, and some can be further divided into iron according to color, hardness and dripping acid. Siliceous and calcareous shale. 3, chemical and biochemical rock: 1) color: gray - grayish white mostly, but often with the mixed matter. 2) Structure: It should be noted whether there are micro-layering and layer structure, whether there are fossils, etc. 3) Structure: If it is crystalline and granular, the coarse, medium and fine particles and their contents should be divided according to the particle size; if it is biological debris, the biological species and its content should be separated. 4) Fracture: It can reflect the degree of consolidation and structure and structure of the rock. For example, if the rock is composed of microscopic calcite or dolomite, the difference of the consolidation is a soil-like fracture, and the consolidation is dense and the shell-like fracture, and the coarser and more uniform particles are “sand-like fractures”. The biological debris is uneven fracture, and if there is microscopic layering, it is stepped. 5) Hardness: generally less than a knife, if mixed with silicon, the hardness increases. 6) Acid reaction: Add acid foaming degree. 7) Naming: Chemical rock and biochemical rock are mainly named according to the composition of the material. The carbonate rock should also be based on the percentage of calcium, magnesium and clay materials (ie, the ease of reaction with hydrochloric acid) and debris. The composition and structure are further subdivided. (II) Description of the identification of the naked eye of the sedimentary rock The rock specimen is observed and described according to the above steps, and the name should be given at the end. To facilitate the reflection of rock features from rock names, the full name of the rock is often used. The general order is: color + construction + structure + composition. The fresh surface of the m specimen is white, the weathered surface is grayish white; the layered structure; the coarse-grained sand-like structure, the particle size is generally about 1 mm, and the gravel with 5%>2 mm is well-rounded, and is mostly rounded and divided. The choice is also better; siliceous cementation. The detrital mineral is mainly quartz, its content is more than 90%, a small amount of feldspar can be seen, and it is kaolin after weathering. According to the principle of naming, the full name of specimen m is: white pebbled coarse-grained quartz sandstone. The n specimen is yellow-green with a small amount of brown spots, muddy structure, compact rock, low hardness, nails can be infused, rough fractures, dull surface, visible fine mica flakes, including trilobites and round cargo fossil fragments, with Parallel book layered texture structure, dripping hydrochloric acid foaming. Specimen n can be defined as: yellow-green containing bio-calcium shale. The q specimen is grayish white, muddy crystal structure, massive structure, rock with shell-like fracture, dense and compact, small knife can be inscribed, localized coarse calcite particles, diameter 1-2mm, cleavage surface glittering, adding hydrochloric acid Intense foaming. Therefore, the q specimen can be determined as: grayish white mudstone. IV. Operation The system describes the following sedimentary rocks: conglomerate, sandstone, shale, marl, dolomite. Identification characteristics of common metamorphic rocks in experiment 9 (3 hours) "Experimental requirements: Through experiments, understanding and basic understanding of the macroscopic identification and description methods of metamorphic rocks, understanding the mineral composition, structural and structural characteristics of metamorphic rocks and identification characteristics of major rock types II. Experimental content and methods: Regional metamorphic rocks: slate, phyllite, schist, gneiss

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