Turn on the power of the polarizing microscope, check and confirm that the lighting system is intact, and gradually adjust the light intensity from weak to strong.
1.2.1 The adjustment of the objective lens is from low power to high power
1.1.2 Specific regulation way is that put some of the rock slices on the stage, adjust the focal length of eyepiece, select a tiny particles to the crosshair center, rotate the object stage to observe the small particles trajectory, then use objective correct screw to adjust for the center, keeping tiny particles remains at the center of the cross wire.Finally, the adjustment is finished. Adjustment of the high power objective lens shares the same way with the low power objective.
1.3.1 The thin section containing biotite is placed under the eyepiece, the strip section of biotite is selected under the plan polarized light, and the object stage is rotated to make the cleavage crack of biotite parallel to the eyepiece cross wire, and the deepest color of biotite is the vibration direction of the lower polarizer. The lower polarized light is generally defined as north – south direction.
1.3.2 After adjusting the lower polarizing light, remove the thin section, and insert the upper polarizing lens, and adjust it to black in the field of view, making the vibration directions of the upper and lower polarizing light be perpendicular (orthogonal) to each other.
First, selecting the quartz particles with full dull and low interference color, place them in the center of the cross wire. Then, the low power objective lens is replaced by the high power objective lens, and put on the spot light and the bertrand lens, and the platform is rotated to show a clear black cross interference diagram. So the microscope is adjusted.
According to the field occurrence, hand specimen observation and preliminary observation under microscope, sedimentary rocks, magmatic rocks and metamorphic rocks are distinguished
3.1.1 Color
To describe the fresh face of rock specimens, the main color is red, yellow, gray, green, black, white, etc., the name of the main color can be prefixed with dark or light, such as light green, dark gray, etc., if there are two colors, it is combined, such as gray yellow, etc.
3.1.2 mineral composition
The minerals of rock specimens are identified and recorded according to their crystal shape, color, luster, hardness and other properties.
3.1.3 Structure
Observe and record the structure of the rock specimens, such as granitic structure, porphyry structure, sandy structure, oolitic structure, lamellar structure, etc.
3.1.4 Hydrochloric acid test
For carbonate rocks or strongly altered rocks, 5% dilute hydrochloric acid solution is generally dropped onto the specimen to observe whether bubbles are generated. If bubbles are present, they contain calcite.
4.1.1 Identification of mineral species
Ways to identify the kinds of mineral:
(1)By observing all the minerals in the thin section using single, orthogonal, and conical light.Based on the optical properties of the transparent minerals in the flakes, Identify all mineral species in thin section. Debris, veinlets, traps etc. of rock composition should be identified and recorded.
(2)The rock thin sections with carbonate minerals were stained with alizarin red solution.
(3)For the complicated, unknown and special significance minerals, other identification methods should be used to further test and identify and further study.
4.1.2 mineral content
There are two approaches for mineral content stastic including Ocular estimation and precise statistical method:
(1)Ocular estimation method: the average mineral content (volume fraction) can be obtained by the estimation of multiple view areas, and the main minerals, minor minerals and accessory minerals can be classified according to GB/T17412(all parts).
(2)Precise count of mineral content (volume fraction) by counter or image analyzer
4.1.3 Characteristics of rock forming minerals
The identification of rock forming minerals should follow the steps below:
（1）Observe and describe the crystal shape, color, twin crystals, inclusion, crushing deformation and secondary changes of rock-forming minerals in detail. Rocks rich in accessory minerals should be given full description .
（2）Assemblage of metamorphic rocks. Symbiotic assemblage characteristics of primary and secondary minerals should be combined. The typical mineral assemblage types of metamorphic facies division of regional metamorphic rocks should be described.
4.2.1 Igneous rock structure division and type
（1）Crystallization degree: idiomorphic crystal, semiidiomorphic crystal, otheromorphic crystal, cryptocrystalline, vitreous
（2） Particle size: coarse grain, medium grain, fine grain, particle, cryptocrystal
（3）The relationship between minerals: arrangement, inclusion, interchange and metasomatism
4.2.2 Structural classification of igneous rocks
4.2.3 Structural division and types of metamorphic rocks
（1）Mineral particle division: variable residual particles, crystalline, cataclastic particles
（2）Structure types: variable residual structure, variable crystal structure, metasomatic structure, cataclastic structure
4.2.3 division and types of sedimentary clastic rocks
（1）Degree of roundness: angular, sub-angular, sub-circular, circular
（2）Particle size: gravel, sand, silt, mud
（3）Types of cementation: basement cementation, pore cementation, contact cementation, filling cementation, regeneration and enlargement cementation
（4）Structure types: terrigenous clastic structure and endogenous sedimentary structure
4.2.4 Structural division and types of pyroclastic rocks
（1）Particle properties: cuttings, crystal chips, glass chips, plastic cuttings, plastic
（2）Particle size: volcanic aggregates, volcanic breccia, volcanic tuff, volcanic dust
（3）Structure type
Rock structure is divided into igneous rock (intrusive rock structure, extrusive rock structure), sedimentary rock (terrigenous clastic rock structure, volcanic clastic rock structure, endogenous sedimentary rock structure), metamorphic rock (metamorphic structure, metamorphic structure, mixed rock structure).
The names of the rocks were determined by the identification of the rock sections according to the GB/T17412 (all parts) rock classification and naming scheme.
6.1 For magmatic rocks and metamorphic rocks, the following steps are carried out:
（1）Mineral identification by polarizing microscope:
It is mainly based on the optical properties of minerals to identify mineral. For instance, observe the color, polychromism, absorption, morphology, cleavage, protuberance and roughness of minerals under single polarized light, and interference color and extinction angle of minerals under orthogonal polarized light, minerals are identified. For some minerals of isomorphic series, their position in the series should be determined according to their special optical properties, such as the identification of plagioclase grade and orthopyroxene series.
（2）Identification of texture and structure
According to the shape and size of mineral crystal grain and their relationship, the texture of rocks is identified. According to the observation of thin sections and hand specimens, the rock structure was identified.
（3）According to the mineral, structure, texture and field occurrence, the rock classification is determined.
The clastic and carbonate rocks in sedimentary rocks are observed as follows:
（1）Clastic rock:
observe clastic (terrigenous clastic, intraclastic, etc.), interstitial (Miscellaneous base, cement) and other characteristics. Rock texture identification: clastic grain size, sorting, roundness, support type, contact mode, cementation type, etc.
（2）Carbonate rocks:
mineral composition and content identification. Identification of fabric components: particle components (particles (debris), mud crystal, bright crystal), in-situ growth biological fabric, self-adhesive fabric, grain structure. Identification of rock structure. Combined with mineral composition, fabric composition and rock structure, the rocks are classified and named.
Identify examples:
CGB/T17412.1-1998 Classification and nomenclature of rocks: Classification and nomenclature of igneous rocks;
GB/T17412.2-1998 Classification and nomenclature of rocks: Classification and nomenclature of sedimentary rocks;
GB/T17412.3-1998 Classification and nomenclature of rocks: Classification and nomenclature of metamorphic rocks;
DZ/T0275.4—2015 Technical specifications for rocks and minerals Part 4: identification of thin sections of rocks
SY/T5368—2016 Rock thin section identification