Identification of Rock Sections

1.1 Mineral Composition Characteristics

1.1.1 Identification of Mineral Species

Ways to identify the kinds of mineral:

(1) Observing all minerals in thin slices by single polarized light, crossed polarized light and conoscopic light, and correctly identified all mineral species in thin slices according to the optical properties of transparent minerals in thin slices. Identify and record rock fragments, veinlets, and captive bodies.

(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.

1.1.2 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.

1.1.3 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.

1.2、Structure of Rock

1.2.1 Igneous Rock Structure Division and Types

(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

1.2.2 Structural Classification of Igneous Rocks

1.2.3 Structural Division and Types of Metamorphic Rocks

(1)Mineral particle division: variable residual particles, crystalline particles, cataclastic particles

(2)Structure types: variable residual structure, variable crystal structure, metasomatic structure, cataclastic structure

1.2.4 Structural 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

1.2.5 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

1.3 Rock Structure

According to the cause, 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).

1.4 Rock Classification and Naming

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.

1.5 Quality Inspection

1.5.1 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.

1.5.2 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. Microstructural identification.

(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.

1.6 Rock Identification Records and Reports

Identify examples:


1.7 Implementation Standard:

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