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The basic content of describing and identifying magmatic rocks with the naked eye is mineral composition and structural structure, which is the basis for classifying and naming magmatic rocks. Secondly, the secondary changes of magmatic rocks should be described, which can reflect the change experience after the formation of the rock. In particular, extrusive rocks are often susceptible to changes. Get a rock and a boat and the order described is: The first is color, followed by structure, mineral composition, structure and secondary changes. The methods and key points to note when describing various features are briefly described as follows:: (1) Color: The color referred to here is the overall color of the rock, not the color of a certain mineral in the rock. Pay special attention to rocks with relatively large mineral particles. It is easy to focus on the color of individual minerals and ignore the observation of the color of the entire rock. Color is not isolated. It is intrinsically related to the type and content of minerals contained in the rock and the chemical composition of the rock. Therefore, color can also roughly reflect the composition and properties of rocks. The color of rocks we observe refers to the general range of hues ranging from dark to light. Common colors of magmatic rocks include black-green-black-dark green (ultrabasic rock), gray-black-gray green (basic rock), gray-gray white (neutral rock), flesh red-light red (acidic rock), etc. Therefore, this kind of rock can be preliminarily classified as basic based on the depth of the color. ； Still neutral ； Or is it acidic? Use this as a factor in comprehensive identification. For eruptive rocks, since its constituent minerals are not easy to identify, it is important to observe the color to help identify the rock. (2) Structural characteristics: The second step is to observe the particle size, shape and combination relationship between the minerals that make up the rock, that is, to understand the structural characteristics of the rock. at the same time. The structural characteristics of the rock appearance reflected by the arrangement and filling of mineral aggregates can be used to distinguish whether the observed rock is plutonic, epigenetic or extrusive rock? If it is a crystalline rock, the mineral particles are generally relatively coarse, and various mineral particles can be clearly distinguished by the naked eye. Generally, they have equigranular structure, unequal granular structure and porphyry-like structure, which are structural characteristics of plutonic rocks. This is basically true whether it is dark or light colored rock. If the mineral particles in the rock are so fine and dense that it is difficult to identify them, and only porphyritic structures, cryptocrystalline structures, and vitreous structures are visible, regardless of the depth of the color, they are generally structural characteristics of extrusive rocks. The structural characteristics of epigenetic rocks and dikes are between plutonic rocks and extrusive rocks, and are often fine-grained, microcrystalline and porphyry. The structural characteristics of magmatic rocks are that most of them have dense massive structures, especially plutonic rocks. However, plutonic rocks sometimes also have streamline flow surface structures, which generally appear at the edges of magmatic rocks, reflecting the relative flow direction of magmatic rocks when they are formed. Extrusive rocks are often characterized by rhyolite structures, pore structures, and almond structures. In particular, rhyolite structures are a significant sign of acidic extrusive rocks. The structural characteristics of epigenetic rocks are also between the two. By identifying the structural characteristics of the rock, we can distinguish whether the rock is plutonic, epigenetic or extrusive, thereby gradually narrowing the scope of its identification. (3) Mineral composition: Further observe the mineral composition characteristics of the rock. This is the most critical and essential aspect. Efforts should be made to identify all the rock-forming minerals in the rock (identification can be based on the physical and chemical characteristics of various minerals and using simple tools such as a knife, magnifying glass, etc.). And roughly visually estimate the particle size and percentage content of various minerals. In order to distinguish which minerals are the main minerals and which are the secondary minerals, record and describe them one by one as the basis for comprehensive analysis and naming of rock characteristics. When observing mineral composition, light-colored minerals should be identified first, and then dark-colored minerals should be identified. Specifically: 1． First check whether there is quartz in the rock and how much is the content. The rock with a high content should be acidic rock, and it must also be in the range of light-colored rock. 2. Then see if there is feldspar present, if it does not contain feldspar. That is to say, the feldspathic rock should be an ultrabasic rock and must belong to the range of dark rock (at this time, if the dark mineral is mainly olivine, it is peridotite, and if the dark mineral is mainly pyroxene, it is pyroxene. ) If the rock contains feldspar, it must be carefully observed to determine whether it is orthoclase or plagioclase, which is more or less, and determine its priority to distinguish acidic rock, neutral rock or basic rock. If it is dominated by orthoclase and contains a large amount of quartz, it can be determined to be acidic rock. If plagioclase dominates, then look at dark minerals. 3． Observe dark minerals. If there is a lot of dark mineral content and it is mainly pyroxene, it is a basic rock. If it is mainly amphibole, it should be a neutral rock. If the rock under observation has been determined to be an extrusive rock based on its structure, ； 1. The matrix should be identified first. At this time, if the mineral composition of the matrix is difficult to identify, it must be identified based on its color depth and rock structure characteristics. 2. Check again whether there are phenocrysts and determine the mineral composition of the phenocrysts. If the crystal is quartz or feldspar, and the rock is light in color, it should be an acidic extrusive rock. If it is definitely plagioclase phenocrysts or dark mineral phenocrysts, it should be a medium or basic extrusive rock. Among them, the one dominated by hornblende phenocrysts is a neutral rock, and the one dominated by pyroxene phenocrysts is a basic extrusive rock. 3. If the phenocrysts cannot be seen in the rock with the naked eye, the rock structure is very fine, and the color is not very standard, then it is difficult to determine which range it belongs to with the naked eye. This situation can only be tentatively classified as fine rock. This must be determined in conjunction with other indoor methods. If it is an epigenetic rock, the color can be used to preliminarily distinguish the properties of microcrystalline or cryptocrystalline. Then focus on observing the types of phenocrysts, such as quartz-type orthoclase phenocrysts, or acidic rock porphyries such as granite porphyry or quartz porphyry. If the phenocryst is plagioclase or dark mineral, it should be porphyry of medium and basic rock type. Among them, the one dominated by hornblende phenocrysts is diorite porphyry, and the one dominated by pyroxene phenocrysts is gabbro porphyry. Finally, the particle size and relative percentage content of various minerals were estimated visually. The above are the steps for identifying magmatic rocks with the naked eye. In addition to the above items, you must also pay attention to the degree of weathering of the rock, the change in color of the weathered surface, the degree of crack development, etc. (4) Comprehensive analysis and rock naming: All materials obtained according to the above steps must be identified and comprehensively analyzed. If it is found that there are inconsistencies in some features among various features, the special contradictions that appear should be carefully reviewed. Whether the contradiction arises due to identification errors. If there is no error in the visual identification after reexamination, the influence of other reasons (such as weathering, alteration or metamorphism of the rock, etc.) should be considered. A certain explanation should be given before sending it indoors for identification and analysis of other instruments. Finally, based on the results of comprehensive analysis. Make a preliminary name for the identified rock as a field name. Generally, the accurate naming of rocks must be coordinated with indoor instrument identification, and the final classification and naming must be made through comprehensive indoor and outdoor research. 2. Examples of describing magmatic rocks: (1) Gabbro (Jinan, Shandong): Dark gray, medium-grained structure, uniform particles, particle diameter generally between 2 and 5 mm, the rock is relatively fresh. The dark mineral is black pyroxene, which is in the form of nearly equiaxed particles, and cleavage lines can be clearly seen on some particles. Some of them have ladder-like cleavage surfaces, a semi-metallic luster, and a dark mineral content of about 50%. The light-colored mineral is plagioclase, which is in the shape of a long plate, white to gray, with a glassy luster. Aggregated twin crystal patterns can often be seen on the flat cleavage surface, with a content of about 50%. (2) Basalt (Nanjing Fangshan): Dark purple-brown, porphyritic structure, the matrix is cryptocrystalline, and has a very clear pore structure, accounting for about 10% of the entire rock, with sizes ranging from 1 to 10 mm, generally 5 to 6 mm. The pores are round to oval in shape, the pore walls are generally smooth and not filled with secondary minerals, and the rock is very fresh. The mineral components of phenocrysts are edinite and plagioclase. Edinite is a brown color derived from the alteration of olivine, with visible flake cleavage and glassy luster. Plagioclase is fine needle-shaped. White to gray, strong glass luster. 3. Experimental content arrangement: Experiment (4): 1. Recognize and describe the following major igneous rocks: (Plutonic rock) Peridotite Olivine Gabbro Diorite Granite Granodiorite 2. Visit the following types of magmatic rocks: Pyroxene Quartz Diorite Chloritized Gabbro Nepheline Syenite Alkaline Syenite (RI501) 3. Tips: (1) Plutonic igneous rocks usually have an equigranular structure, and some have a porphyry-like structure, but the matrix is all crystalline. (2) Ultrabasic → basic → neutral → acidic color: Deep——————————→ Light Quartz: (Content) None————A small amount————One——→ Many dark minerals: Olivine→pyroxene→hornblende→biotite feldspar: Basic plagioclase → neutral plagioclase → potassium feldspar and acidic plagioclase