Petrology is the branch of geology that studies rocks which include the formation and dissemination. Is a constituent of the earth's rocks. In the field of petrology, also known as the term rock cycle (rock cycle) cycle where it explains how the rock cycle.
Magma
Liquid silicate magma is incandescent that is mobile and has a temperature of between 900 - 1200 oC. possess a dominant magma composition of Si, Al, Mg, K, Fe, ca, Na, H, O. Located at the bottom of the earth's crust or upper matel (FF. Grouts, 1947; Turner and Verhogen 1960, H. Williams, 1962) . Magma is the material that fills the magma chamber, from a volcano. Magma that reaches the Earth's surface is called lava.
Process Formed
The process of magma formation occurs as a result of rock senagai pressure and temperature are very high. At the mid-ocean ridge (Mid Oceanic Ridge) magma comes out as lava, which then form a new rock. Magma can also exit in the continental crust as a result of the subduction of the oceanic plate continental plate, which is then due to temperature and very high pressure, the oceanic plates become magma again.
In the process perjalananya toward the surface, the magma will be in different conditions than before as a decrease in pressure and temperature, so it will have a further differentiation can alter the composition of the magma becomes homogeneous certain minerals minerals. The process of differentiation processes that occur in magma include:
Fragsinasi
Separation is the process of separating elements with different compositions in the magma into the group - similar groups through the process of crystallization. This terhadi because some elements of the element has a different freezing point - different.
- Gravity setling / Crystal setling
Crystals Crystals heavy as Fe, Mg and Ca which has undergone freezing was accumulated at the bottom of the magma body due to the influence of gravity.
- Liquid Immisibility
Immisibility liquid separation process solution is a solution of magma that has different properties and composition.
- Crystal Floatation
This process will cause the crystals crystals that have a lighter specific gravity will float at the top of the magma body
- Diffusion
In the course of the magma towards the surface, the magma will menorobos rock wall rocks in its path, it may cause meluburnya wall rock mixed with a solution of the magma when the magma temperature higher than the freezing temperature of the rock. The quantity of rock dissolved in magma magma determine the intensity of the change itself.
Composition of Magma
Magma possess various chemical compositions, generally described as oxides such as SiO2, Al2O3, CaO, TiO2, and H2O. The composition of the magma can be divided into 3 groups, namely:
- Major Element
Is the main element forming magma, a non-volatile compound which is a compound element oxides with the percentage reaches 99%. Unsu elements are oxides: SiO2, Al2O3, Fe2O3, FeO, MnO, CaO, Na2O, K2O, TiO2, and P2O5
- Minor Elements
The element is the bit of the body that magma is volatile, with a fraction of the gas fraction in the form of CH4, CO2, H2S, HCl, and SO2.
- Trace Elements
Trace elements are elements of a very little bit amount in the magma, such as the elements Rb, Ba, Sr, Ni, CO, V, Li, Cr, S and Pb.
Magma may have evolved, so it can change the nature and composition of the magma origin through processes such as:
- hybridization
Mixing of two different types of magma properties and composition, such as the acid magma has a high visikositas (thick) mixed with alkaline magma that has a low visikositas (diluted) with the same relative persentasti magma would form intermediate (middle) with a viscosity that is.
- Assimilation
This process occurs due to magma mixing traversed the rock side, this can occur if the temperature of the magma broke through rocks is higher than the temperature of the melting point of the rock.
- Anateksis
Anateksis is the process of formation of new magma from the melting of rock at very deep depths. It is a very dominant role in this process is temperature and temperature are very high.
Rock Cycle
Cycle rock (Rock cycle) is a process that occurs in rocks in a very long time span. This can explain about how the genesis of rock, and distribution. Endogenous and Exogenous energy is very influential terrhadap the course of this process. Further explanation can be followed by a more detailed elaboration as follows:
a. Magma - Igneous Rock
The formation of igneous magma into the initial stages of this process, where magma rises to the surface freezes to form a wide variety of minerals. Minerals are minerals collected and then formed through the process of crystallization of igneous rocks.
b. Igneous rock - Sedimentary Rocks
Igneous rock that emerged surface will be deposited by the processes that influenced the style of exogenous (outside asa style), such as weathering (weathering), erosion (erotion), transport (Transportation), Deposition (sedimentation), and pembatuan (lithification). Media transport media that play a role in the transport process may be water, wind, glaciers (ice) etc..
c. Sedimentary rocks - Metamorphic rocks
Sedimentary rock is formed can be altered talah of physical and chemical composition when under pressure and very high temperatures through the solid phase into metamorphic rocks. This process is referred to as metamorphism.
d. Igneous rocks - Metamorphic rocks
Igneous rocks can be directly transformed into metamorphic rocks of sedimentary rock without having to be first. This is the condition where the igneous rock under pressure and extremely high temperatures that alter the physical properties and chemical composition of the early through the solid phase.
e. Metamorphic rock - Sedimentary Rocks
Metamorphic rock can undergo emerged surface weathering, erosion, transportation, sedimentation and sedimentary rocks litifikasi be back
f. Igneous rocks - Magma
Igneous rocks can also be melted into magma again when met with the magma itself, either through a process of assimilation and anateksis process. Provisions applicable here is when magma broke through rocks that have a temperature and pressure that is higher than the melting point of the rocks themselves
g. Sedimentary rocks - Magma
Similarly, igneous, sedimentary rock can then also melt into magma again through the process of assimilation and anateksis.
h. Metamorphic rocks - Magma
Metamorphic rocks can back into magma when under pressure and temperature higher than the melting point of rock meramorf itself.
Classification of Rocks
In general, rocks that are in the good earth is exposed on the surface of the earth or inside the earth is divided into 3 major groups, namely igneous, sedimentary, and metamorphic rocks. The three groups have different formation processes - different and different distributions. Classification of igneous rocks is intended to facilitate the identification poses a rock. All three rock types has a different mineral composition - different.
Igneous rocks
Igneous rock formed from magma that cools the freezing process. Igneous rocks can be formed on the surface of the earth as volcanic igneous rocks (igneous rocks outside) or Plutonic igneous rocks (in igneous rock). These rocks can form crystals (Holokristalin), glass (Holohyalin), or both (Hipokristalin). Igneous rocks have traits that hard, so it is quite easy to recognize these rock types in the field.
The process of formation of igneous rock (Genesis)
The process of formation of igneous rock formed by cooling magma. At this stage of the constituent minerals of igneous rock minerals begin to form in accordance with the conditions of its formation, respectively. For ease of explanation, the bowen make a hypothesis about the sequence of mineral formation of igneous minerals suitable temperature and composition of the rocks. Assuming that only comes from a single magma types.
On the right (Continues Series)
In this section first minerals formed at temperatures 1200OC is anortit, followed labradorite, and oligoklas. This group is a group of Ca-Plagioclase from alkaline magma saturated with Ca content At a later stage at a temperature between + 900oC - 800oC, the magma began to change the nature of a mineral forming intermediates andesine, bitownit and albite. This group is also a group called Na-plagioclase. Lastly, having a meeting with the left (discontinuous Series) orthoklas forming minerals, muscovite and quartz. The group was formed at a temperature of 750oC + with acids.
On the left (discontinuous Series)
In the left part of the picture, this group is a group formed by magma that is saturated will content of Fe, Mg. Olivine is a mineral that was first formed at temperatures 1200OC then followed by the mineral pyroxene. This group is a group of alkaline minerals. At lower temperature minerals formed Hornblende and biotite. This group is a mineral intermediates. In the final stage a meeting between the group on the right (Continuous Series) with a group on the left (discontinuous Series) at a temperature of 750oC forming mineral + Ortoklas, Muscovite, and Quartz acidic.
Classification of Igneous Rocks
Classification of igneous rocks is intended to facilitate the identification of the igneous rocks. There are 2 main runway is applied in the classification of these rocks, namely:
- Classification Based on the formation Places
This type of classification is based on the location of the formation in this case is the depth, produces 2 types of igneous rocks, namely:
1. Igneous Rocks In (Plutonic)
The igneous rocks formed at relatively deep depths, the cooling process is running very slow, thus allowing for the formation of crystals Crystals. This type of igneous rock has a rough texture traits (faneritik) so it is quite easy to identify. This type of igneous rock is Granite, Granodiorite, diorite, peridotite and Dunit.
2 Igneous Rocks Outside (Volcanic)
This kind of igneous rocks formed at relatively shallow depths to the surface even. Crystal formation process runs quickly even in a state that is very fast so do not have time to form crystals produce glass (Holohyalin). The texture of the igneous rocks of this type is relatively more subtle (afanitik) and glass. Examples of this type of rock is basalt, andesite, and obaidian ryolit.
Classification Based on Chemical composition
The classification of this type tend to be more effectively used and most frequently used. The classification of the underlying on the chemical composition of the constituent minerals. This type of classification produces 4 main groups of igneous rocks, namely:
1. Ultramafic Igneous Rocks
This igneous rock has a composition of silica which is less than 45%, the MgO content of more than 18%, and high content of FeO. Mineral constituent of these rocks are generally minerals olivine and pyroxene. Examples of this type of igneous rock is Dunit, peridotite, harzburgit, lherzolit, and Pyroxenit.
2. Mafic Igneous Rocks
Igneous rocks of this type have a silica content between 45% to 52%. Igneous rocks of this type are generally dark in color, as compiled by the dominant mafic minerals. The rocks constituent minerals are olivine, pyroxene, hornblende, biotite, plagioclase and quartz. With basalt rock samples, anortosit, gabbro,
3. Intermediates Igneous Rock
The igneous rocks have a silica content between 52% to 66%. The composition of the igneous rocks of this type are generally biotite, plagioclase, muscovite and quartz. Cirri igneous rocks of this type has a color which is (between dark and light, usually gray). Examples of this type of igneous rock is andesite, and diorite
4. Felsic Igneous Rock
The igneous rocks have a high silica content, more than 66% resulting in a relatively bright color. General composition of this rock type is Ortoklas, Muscovite, plagioclase and quartz. Examples of this type of rock is granite, Ryolit, Granodiorite.
Identification of Igneous Rock
Identification of an igneous rock identification method that can be used with the based on physical appearance, as well as the mineral composition penyusunya clams. Here are some of the parameters - the parameters used, including:
1. Color
Color is a parameter that is used to identify igneous rocks, because observations of color can easily be seen without a microscope though. Colors can be divided into two, the color used on the exterior weathered rocks that have been affected by external forces. In some cases it can change the color of the original (sometimes not). Color fres (in situ) is the original color of the rock. To determine the original color usually have to find a rock fres, or can be seen by the way in the first part crushed rock to see the original color in it. Color rocks characterize the mineral content contained therein, even can be used as an additional determination of rock name, for example: bright gray andesite.
2 Texture Rocks Frozen
Texture is a parameter used to identify igneous rocks that can be seen megaskopis (naked eye) and microscopic (under a microscope). There are several parameters that are used in the identification of igneous rock textures including:
Crystallization degrees
This parameter is used to measure the number of crystals terkadung in igneous rocks, which is expressed in type:
- Holokristalin
Holokristalin naming degrees is used for the crystallization of igneous rocks composed leh Crystals Crystals.
- Hipokristalin
Hypo crystalline crystallization degrees constituent is composed of a mass of rock crystal and glass mass
- Holohyalin
Holohyalin degrees crystallization is used to menyataka igneous rocks composed of glass mass.
granularity
Granularity is one of the parameters used to determine the grain size in igneous rocks. It can provide information about the formation of these igneous rocks (relatively deep or relatively shallow). Sometimes circumstances granularity a rare igneous rock, often used as an adjunct in the naming of rocks, such as andesite porphyritic / porphyry. Granularity igneous rocks are divided into three groups, namely:
- Fanerittik
Faneritik used to declare the size of the crystal grains are relatively large / coarse, and can be observed megaskopis. It characterizes that the plutonic rocks of the manifold (in igneous rock).
- porphyritic
Porphyritic used to express the crystal grain size is, where there can not be diammati crystals and crystals that can be observed directly.
- afanitik
Afanitik used to express the crystal grain size is relatively small / very small (tdak can be observed directly). This indicates that these types of igneous rocks are igneous volcanic (igneous outside), with a relatively fast freezing speed.
- Glassy (Glass)
used to express the rock mass composed by the glass entirely. Example: obsidian.
Form of Item
Grain shape on the claim form igneous rocks of the crystal itself. There are 3 types of grain shapes in igneous rocks, namely:
- If euhedral crystals form in igneous rocks have a perfect crystal field
- Subhedral crystals form when the mineral is limited by the field of a perfect crystal
- Anhedral crystals form when the mineral is limited by imperfect crystal field
3. Structure
The structure of igneous rocks can be interpreted as the appearance of the different parts of the rock. This is a picture of the body of igneous rock, with a broader spectrum of the structure in question is usually the appearance of outcrops in the field. Structures found in igneous rocks, usually in the form of:
- Masive, this structure is the appearance of igneous rock states that do not have the appearance of other structures structural (solid)
- Jointting, if the appearance of the igneous rock cracks are cracks
- Vasikuler, if there is a vent hole interconnected. This vent hole created by the evaporation of gas content in the magma at the time of freezing
- Scoria, if the gas vent hole unrelated
- Xenolith, a structure which reveals rock fragments in it as a result of condensation is not perfect.
- Amigdaloidal, this structure is formed when the gas vent hole that has been left behind, in the content returned by other minerals.
- Joint Sheeting, an igneous rock structures that reveal the layers as a result of the intrusion is parallel to the rock layers in the breakthrough (concordant)
- Columnar Joint, this structure occurs as a result of intrusion of magma broke through in the opposite direction to the layers of rock that intruded. The appearance of these structures in the field a stocky columns.
to be continued..
