Mineral composition of magmatic rocks, mineral composition of sedimentary rocks

7 Magmatic Rock and Magmatic Rock Composition.

7 Magmatic Rock and Magmatic Rock Composition.

More than 160 minerals have been found in sedimentary rocks, but only about 20 are major and recurring. Such as siliceous minerals (quartz, chalcedony, opal, etc.), clay minerals (illite, montmorillonite, kaolinite), mica minerals, feldspar minerals, carbonate minerals, etc. These minerals account for about 98% of the total mineral composition in sedimentary rocks.

In addition, oxides and hydroxides of iron and manganese, phosphate minerals and sulfate minerals are also common in sedimentary rocks (Table 7-4).

Table 7-4 Average mineral composition of sedimentary and magmatic rocks (%)

As can be seen from Table 7-4, the mineral composition of sedimentary rocks is different from that of magmatic rocks, mainly as follows:

1) Minerals that are very rare or almost non-existent in sedimentary rocks are: olivine, feldspar, common hornblende, pyroxene, etc. However, these minerals are ubiquitous in magmatic rocks.

2) Clay minerals, salt minerals, carbonate minerals, organic matter, etc. are the characteristic minerals of sedimentary rocks and the main mineral components of sedimentary rocks.

3) Acid plagioclase, potassium feldspar, quartz, muscovite and other minerals exist in both magmatic and sedimentary rocks, but the content varies greatly.

The minerals that make up sedimentary rocks can be divided into the following types according to their formation stages: terrigenous clastic minerals, syngenetic minerals, diagenetic minerals and metagenetic minerals. Syngeneous minerals, diagenetic minerals and metagenesis minerals are all generated in the process of sedimentary rock formation, so they are also collectively referred to as autogenous minerals.

1) Terrigenous clastic minerals: ** in weathered original rocks, which existed before the formation of sedimentary rocks, so they are also called inherited minerals. Quartz, feldspar, muscovite and heavy minerals such as zircon, garnet, apatite, rutile, and staurolite are common.

2) Synbiotic minerals: refers to minerals formed by precipitation from colloidal solution or true solution. Such as various salt minerals (rock salt, potash, carnallite, etc.), authigenic clay, aluminum, iron, manganese oxides and sulfides, colloidal phosphate rock, glauconite, etc.

3) Diagenetic minerals and metamorphic minerals: mainly zeolite, metagenetic dolomite, authigenic quartz, austemic fossil, etc.

1. Silicon-aluminum minerals: SiO2 and Al2O3 are relatively high, excluding FEO and MGO, including quartz, feldspar and quasi-simple feldspar. These minerals are lighter in color, so they are also called light-colored or light-colored minerals.

2. Iron and magnesium minerals: the content of FeO and MGO is high, and the content of SiO2 is low. These include peridot, pyroxene, hornblende and biotite. These minerals are generally darker in color, so they are also called dark or dark minerals.

7 Magmatic Rock and Magmatic Rock Composition.

Minerals are classified according to their role in the classification and nomenclature of magmatic rocks: major minerals, minor minerals, secondary minerals. Major minerals refer to minerals that are abundant in the extension and play a major role in determining the name of the extension category.

Minor minerals are minerals that are less abundant in rocks than primary minerals. Paraminerals are minerals that are present in very small quantities in rocks and do not play a role in the general classification and nomenclature of rocks.

Classified according to the color and chemical composition of minerals: dark minerals, light minerals.

For example, quartz and feldspar are white or flesh-colored, and are called light-colored minerals. Aluminum silicone minerals, also known as light-colored minerals, refer to minerals with high content of SiO2 and Al2O3 and no iron magnesium. Such as quartz, feldspar, etc.

Peridot, pyroxene, hornblende, and mica are dark green, dark brown in color and are known as dark minerals. Iron and magnesium minerals, also known as dark minerals, refer to minerals with high content of FeO and MGO and low content of SiO2. Minerals such as olivine, pyroxene, hornblende and biotite.

According to the classification of mineral genesis: acoustic minerals, allogenesis minerals and secondary minerals. Primary minerals are minerals that are formed during the crystallization of magma.

Allophytic minerals are minerals formed by the assimilation of magma into surrounding rocks and captives to change their composition. Secondary minerals refer to new minerals formed after magma formation, due to weathering and hydrothermal alteration after the magmatic period.

Magmatic rocks, also known as igneous rocks, are rocks formed by magma erupting from the surface or invading the earth's crust for cooling and solidification, with obvious mineral crystal particles or pores, accounting for about 65% of the total volume of the earth's crust. Magma is a hot, hot, viscous, volatile silicate melt produced deep in the earth's crust or upper mantle. It is the matrix for the formation of various magmatic rocks and magmatic deposits.

The whole process of magma generation, migration, accumulation, change and condensation of rocks is called magmatism.

Composition of magma: mainly silicate material, only a few volcanoes have ever erupted carbonate magma (e.g., eastern Tanzania, Africa) and iron oxide magma (e.g., Chilean Laco magnetite magma in South America). There are a large number of oxygen, silicon and other elements in the silicate slurry, which form a complex anion cluster in various states in different forms and silicon-oxygen tetrahedrons.

Extreme conditions of magma.

1. High temperature The magma temperature is about 900 -1400, which is close to the melting point of iron!

2. Classification Magma is divided into primary magma and regenerated magma, of course, from this term, it can be basically understood that the primary magma comes from the core of the earth, and the regenerated magma is the molten magma produced in the plate movement cycle, and the depth and composition of the two are somewhat different.

3. Viscosity The composition of magma is different, and its viscosity is also different! The higher the silica content in the magma, the more viscous it will be! For example, the olive basalt flow in Hawaii has a viscosity at 1100 and a flow velocity of 400 m h at a slope of 2°!

It is about 4-5km h for the average person, so it is easy to exceed the magma flow speed on foot! But the problem is that if the slope is too steep or the magma detours ahead, something big may happen!

7 Magmatic Rock and Magmatic Rock Composition.

Composition of magma According to the lava spewed out by modern volcanoes, silicates are the main component of magma. The content of SiO2 is between 80 and 30%; Metal oxides such as AI2O3, Fe2O3, FeO, Mgo, CaO, Na2O, etc., account for 20-60%. Others, such as heavy metals, non-ferrous metals, rare metals and radioactive elements, the total amount of which does not exceed 5%.

In addition, magma also contains some volatile components, mainly H2O, CO2, H2S, F, Cl, etc.