Petrology

ORIGIN OF PETROLOGY

There are different minerals or different proportions that can give rise to different types of rocks. There are different types of rocks having the same minerals but are in different proportions.

Rocks can be classified based on different principles such as physical classification, chemical classification, and geological classification. Among the three, geological is the most proper because grouping of rocks is more orderly and comprehensive.

Rocks can also be classified as igneous, sedimentary, and metamorphic.

igneous rock

Igneous rock is formed through cooling and solidification of lava or magma. It can be derived from partial melts of existing rocks and the melting can be caused by one or more melting processes. These include temperature increase, decrease in pressure, and change in composition.
Solidification of igneous rock can occur as intrusive (occurs below the surface) or extrusive (on the earth's surface).

SEDIMENTARY rock

Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms. They can be formed from deposits that once accumulated on the earth's surface. They make up 7.9% of the Earth's crust and 66% of the Earth's surface.
There are three major types of sedimentary rocks, these are clastic, biochemical and chemical sedimentary rocks.

TYPES OF SEDIMENTARY ROCKS

CLASTIC

It is the most common type of sedimentary rock. These are sandstones formed from clasts or pieces of other rocks

BIOCHEMICAL

These are formed from hard biological material that are compressed

CHEMICAL

These rocks are formed from chemical precipitation. A chemical precipitate is a chemical compound formed when solution is dissolved in evaporates

METAMORPHIC ROCK

Metamorphic rocks are rocks whose texture and composition was changed due to metamorphism. These rocks undergone change due to intense heat and/or pressure. Also, metamorphism of rocks is subdivided into two types, contact and regional metamorphism.
Contact metamorphism is a change driven primarily by intense heat, while Regional metamorphism is driven primarily by intense pressure.
Metamorphic rocks are often found deep in the Earth's crust or at plate boundaries where tectonic plates collide.

PROPERTIES OF ROCKS

Igneous rocks

They all contain minerals
Majority is made up of silicate materials
The process of rock formation cannot be observed directly
They can be fine-grained or coarse-grained
Glassy Texture

sedimentary rocks

(Sedimentary rocks vary slightly from rock to rock)

Clastic Rocks are formed from small pieces of fragmented rocks deposited then lithified by compaction and sementation
They are found mostly on the Earth's surface
They contain fossil records of ancient plants and animals

metamorphic rocks

They are crystalline and have a squashed texture
Generally crystalline in texture
Have a banded or squashed look
Do not get hot enough to melt

DISTRIBUTION OF IGNEOUS, SEDIMENTARY, AND METAMORPHIC ROCKS

IGNEOUS ROCKS - Because of their origin under conditions of high temperature, they are considered as unfossiliferous

granite

Granite forms when magma cools relatively slow underground

SYENITE

They have the same general composition as granite but with either absent or lesser quarts
Formed when a granitic or igneous rock undergoes fairly low degree of partial meltiing

DIORITE

Group of coarse-grained igneous rock with composition between granite and basalt. It occurs as large intrusions, dikes and sills within continental plate

PEGMATITE

These are extreme igneous rocks that form during final stage of magma's crystallization

dolerite

An igneous rock exposed over half of tasmania. It cools under basaltic volcanoes like those at mid-ocean ridges.

BASALT

It is dark-colored , fine-grained igneous rock composed mainly of plagioclase and pyroxene minerals. It has the same composition with gabbro just it was fine-grained

SEDIMENTARY ROCKS - Sedimentary rocks are formed by accumulation of sediments

sandstones

These are sedimentary rock composed mainly of sand-size mineral or rock grains. They are formed from cemented grains that maybe fragments of pre-existing rocks or crystals of a single material

limestones

These are composed primarily of calcite, and produced mainly by marine organisms.

shales

It is a fine-grained rock that is formed from clay or mud. It contains fossils and often form reservoirs of petroleum and other hydrocarbons

conglomerate

These are made up of rounded clasts that are greater than 2mm in diameter

breccia

It is composed of large angular fragment, which is commonly located at the base of an outcrop where mechanical weathering debris accumulates

METAMORPHIC ROCKS - These are existing rocks transformed to a new type of rock through the process of metamorphism

quartzite

It is composed almost entirely of quartz. Most quartzite was formed during mountain-building events at convergent plate boundaries

marble

It is formed when limestone was subjected to heat and pressure. Some of these rocks were formed by contact metamorphism

slate

These rocks are created by the alteration of shale or mudstone by low grade regional metamorphism

gneiss

It has bands and lenses of varying mineral composition. It is formed by regional metamorphism at convergent plate boundary

schist

It is made up of plate-shaped mineral grains that are large enough to see with the naked eye. It is formed on a continental side of convergent boundary subjected to intense forces, heat, and chemical activity

assignment submitted in module 3:

Assignment #3_BARTOLOME.pdf

coursework #3

Coursework #3_BARTOLOME.docx

reflection:

This module tackles the different types of rock based on geologic classification systems. Also, it entails the overall explanation about petrology and formation of rocks (igneous,sedimentary,metamorphic). After watching the video presentation by Group 3, I have grasped lots of realizations on how rocks can be classified based on physical, chemical, and geological classification. I learned that rocks have their distinct, but share the same characteristics and properties based on their geological classification, whether if they are igneous, sedimentary, or metamorphic. Thus, these classification of rocks also have their own distribution. For example, igneous rock are considered unfossiliferous unlike sedimentary because they are formed under high temperature. Although these things are already familiar since they were already discussed during my high school years, there are some subtopics which seemed unfamiliar to me (e.g. types of metamorphism and distribution of rocks).

Lastly, I learned that petrology plays an important role in ascertaining the physical and chemical composition of rocks and the different conditions that influence their formation. Although rocks constitute different minerals, making them heterogenous, it will become easier for us to study and understand their nature of formation due to background knowledge in petrology.

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