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Rocks: Types with Examples & Properties

 Types of Rocks with Examples

Different Types of Rocks and their Properties:
» A rock is made up of two or more minerals and can also contain organic compounds.
» Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids.
» For example, granite, a common rock, is a combination of the minerals quartzfeldspar and biotite.
» Minerals are obtained from rocks.
» The Earth's outer solid layer, the lithosphere, is made of rock.
» The scientific study of rocks is called petrology, which is an essential component of geology.
» Rocks occur in different shapes, colours, weights, strengths, sizes, and texture.
» Rocks also change from one form to another and differ from one region to another because of the rock cycle.
» These changes usually take thousands or millions of years. Rocks are also mainly porous or non-porous in nature.
» Rocks may not always necessarily be hard.
» Geologists classify rocks into three groups, according to the major Earth processes that formed them.
» The three different types of rocks are Igneous, Sedimentary, and Metamorphic. The difference between each type is in how they are formed.

Types of Rocks

1.       Igneous Rocks
2.      Sedimentary Rocks
3.      Metamorphic Rocks

Igneous Rocks

» Igneous rocks are found by volcanoes and in mountain belts
» Such rocks form when magma (molten rock) cools and solidifies.
» Igneous rocks are harder and granular.
» Plutonic or Intrusive and Volcanic or Extrusive are two different type of Igneous rocks
» Volcanic or Extrusive igneous rocks are those formed when magma reaches the surface (at which point it is called lava), cooling and solidifying quickly. Example: Basalt
» Plutonic or Intrusive igneous rocks are formed when magma slowly cools deep below the surface of the earth. Different sized grains form, depending on the conditions of the rock formation. Example: Granite
» Intrusive rocks are generally more coarse-grained than extrusive. Coarse grains are more than 3/16 of an inch; medium grains, 1/64-3/16; and fine grains, less than 1/64 of an inch.
» Igneous rocks have many distinct characteristics.
» For example, light-colored igneous rocks are more acidic and have over 65% silica.
» Dark-colored rocks are more basic and have a higher percentage of ferromagnesian minerals.
» Igneous rocks are broken up into three main groups: acid, intermediate, and basic. Acid rocks have over 65% silica, intermediate rocks have 55-65% silica, and basic rocks have 45-55% silica.
» There are no layers in Igneous rocks
» Examples of Igneous Rocks:
·    Gabbro, Granite, Rhyolite, Obsidian, Diorite, Felsite, Tuff, Scoria, Andesite, Basalt, Peridotite and Pumice are all examples of igneous rocks.

Sedimentary Rocks

» Sedimentary Rocks are formed when rocks ‘settle out’ of water or air.
» These rocks form when layers of sand and pebbles are compressed enough to form rock.
» The particles that form a sedimentary rock by accumulating are called sediment.
» Fossils are mainly found in sedimentary rock, specifically limestone because limestone is formed in warm, shallow seas and organisms and shells get fossilised at the bottom.
» There are three different grain sizes in sedimentary rock. Coarse which you can see with the naked eye. Medium which you can see with a hand lens, and fine which you can see with a microscope.
» There are 3 Types of Sedimentary Rocks
1.       Chemical
2.      Detrital
3.      Biogenic
» Chemical Sedimentary Rock refers to rocks containing minerals produced by chemical precipitation.
» Chemical sedimentary rocks are derived from material carried in solution to lakes and oceans.
» Under certain conditions, the dissolved material precipitates out of solution and, thus, settles to the bottom.
» Precipitation may occur due to physical processes such as evaporation or through living organisms.
» For example, limestone is the most abundant chemical sedimentary rock, and it's typically formed when calcite precipitates due to evaporation.
» Calcite is produced by living organisms to form shells which can, in turn, form sedimentary rocks. Now, interestingly, 90% of limestone is of this biological origin.
» Detrital Sedimentary Rock refers to rocks which contain particles from preexisting rocks. Sedimentary rock can form as solid particles from weathered rocks.
» These particles are called detritus, and detrital sedimentary rocks are accumulations of detritus.
» Therefore, the source of sediment for detrital sedimentary rocks is weathered rock from another form.
» For example, particles of sand from other rocks can form sandstone, and mud can form shale, which is the most common form of sedimentary rock.
» Biogenic Sedimentary Rock contain fossil and shell fragments.
» Examples of Sedimentary Rocks
·   Sandstone, Shale, Limestone and conglomerate are all examples of sedimentary rocks.
» Limestone is white as well black.
» Sandstone is dull white, pink, bright red or sometimes black.
» Igneous and sedimentary rocks are largely prevalent in the world

Metamorphic Rocks

» A metamorphic rock is a result of a transformation of a pre-existing rock.
» The original rock is subjected to very high heat and pressure, which cause obvious physical and/or chemical changes.
» Metamorphic rocks form when rocks are subjected to heat and pressure, but not to the point of melting.
» Depending on whether it was formed under just heat or heat and pressure the orientation of the crystals will be different.
» Contact metamorphic rocks are formed in just heat and crystals are randomly arranged.
» Regional metamorphic rocks are formed in both heat and pressure and have crystals that are aligned.
» The greater the pressure and temperature these rocks are exposed to the larger the grains.
» Medium to high-grade metamorphic rocks occurs at a minimum temperature of 480 degrees f and a maximum temperature of 1,472 degrees f but can be much lower.
» Examples of metamorphic rocks are:
   Slate, Marble, and Granulite.
» Some examples of metamorphic rocks formed from igneous and sedimentary rocks are:
Type of Rock
Original Rock
Metamorphic Rock
Graphite Coal
Shale/ Clay
Slate, Mica Schist

» The study of metamorphic rocks provides information about the temperatures and pressures that occur at great depths within the Earth's crust.
» Some examples of metamorphic rocks are gneissslatemarbleschist, and quartzite.
» The layering within metamorphic rocks is called foliation (derived from the Latin word folia, meaning "leaves"), and it occurs when a rock is being shortened along one axis during recrystallization.
» Foliated metamorphic rocks appeared bent or layered. Example: Mica.
» Non-foliated metamorphic rock usually contains one mineral. It is uniform in texture. Example: Quartzite and marble.

Important Questions asked in Various exams Related to Different Types of Rocks

1. Which one among the following rocks does not belong to the same group?
a. Shale
b. Limestone
c. Slate (Correct Answer)
d. Sandstone
2. The Deccan Trap Formation was caused by
a. Shield eruption (Correct Answer)
b. Composite eruption
c. Caldera eruption
d. Flood basalt eruption
3. In which among the following terrains the bore wells and canals can be dug easily?
a. Gneiss, granites and basaltic terrain of Peninsular India
b. Rolling and dotted hilly terrain of North-east India
c. Soft alluvium of the Northern Plains (Correct Answer)
d. Confined aquifer below the normal water table
4. The Damuda series of Gondwana system has three stages, namely, Raniganj, Barren Rocks and Barakar. The middle stage is called Barren because
a. it consists of coal and not iron
b. it consists of iron and not coal
c. it consists of neither coal nor iron
d. it is a sedimentary layer consisting of shale and clay (Correct Answer)
5. Which of the following statements is/are correct?
1. The major constituent mineral of granite rock is quartz.
2. The major constituent mineral of sandstone rock is feldspar.
3. The major constituent mineral of limestone rock is dolomite.
Select the correct answer using the code given below:
a. 1, 2 and 3 (Correct Answer)
b. 3 only
c. 1 and 2 only
d. 2 and 3 only
6. Which one among the following is a primary rock?
a. Sedimentary
b. Igneous (Correct Answer)
c. Metamorphic
d. None of the above
7. Which of the following statements regarding the Deccan Trap is/are correct?
1. Intense volcanic activity in the form of fissure eruption took place towards the end of Cretaceous period
2. The volcanic lava spread out in horizontal sheets
3. The regur soil found here is rich in nitrogen
Select the correct answer using the code given below:
a. 1 and 2 only (Correct Answer)
b. 1, 2 and 3
c. 3 only
d. 1 only
8. Consider the following statements about rocks:
1. Shale becomes Slate through metamorphosis
2. Shale is converted to Slate when it is subjected to tremendous pressure and high temperature
Which of statements given above is/are correct?
a. 1 only (Correct Answer)
b. 2 only
c. Both 1 and 2
d. Neither 1 nor 2
9. Which one of the following is generally found in sedimentary rocks?
a. Basalt
b. Silica (Correct Answer)
c. Shale
d. Magnesium
10. The earth’s crust is the thinnest
a. under the mountain ranges
b. under continental masses
c. at ocean bottoms (Correct Answer)
d. at mid-oceanic ridges
11. Which of these is not responsible for the formation of igneous rock?
a. sediments (Correct Answer)
b. liquid rock
c. magma
d. lava
12. Which of the following rocks is different from others?
a. marble (Correct Answer)
b. gypsum
c. sandstone
d. limestone
13. Magma that cools slowly beneath the earth's surface produces
a. ore minerals.
b. intrusive igneous rocks. (Correct Answer)
c. fine-grained metamorphic rocks.
d. extrusive igneous rocks.
14. Igneous, sedimentary, and metamorphic rocks are usually composed of
a. intergrown crystals
b. minerals (Correct Answer)
c. fossils
d. sediments
15. Which process is necessary for the formation of igneous rocks?
a. erosion
b. deposition
c. metamorphism
d. solidification (Correct Answer)
16. Which characteristic of rocks tends to increase as the rocks are metamorphosed?
a. density (Correct Answer)
b. porosity
c. permeability
d. number of fossils present
17. In which type of rock would you expect to find fossils?
a. granite
b. obsidian
c. shale (Correct Answer)
d. marble
18. Which of the following is true about rocks?
a. Rocks are composed of only one mineral.
b. Rocks do not contain minerals.
c. Coal is not considered a rock.
d. Most rocks are a mixture of minerals. (Correct Answer)
19. Which of the following is NOT one of the three types of rock?
a. Igneous
b. Sedimentary
c. Magma (Correct Answer)
d. Metamorphic
20. Metamorphic rock forms as a result of
a. Heat and pressure (Correct Answer)
b. The cooling of magma
c. Compaction of sediments
d. The melting of rock
21. A rock that forms when magma hardens beneath Earth's surface is called an
a. Intrusive metamorphic rock.
b. Intrusive igneous rock. (Correct Answer)
c. Extrusive sedimentary rock.
d. Extrusive igneous rock.
22. Which of the following is an example of an extrusive igneous rock?
a. Basalt (Correct Answer)
b. Coal
c. Sandstone
d. Granite
23. Lava that cools so quickly that crystals do not have time to form will lead to igneous rocks with a
a. Porphyritic texture.
b. Coarse-grained texture.
c. Glassy texture.(Correct Answer)
d. Fine-grained texture.
24. Which of the following represents the correct order of the processes responsible for the formation of sedimentary rocks?
a. Erosion, weathering, compaction, cementation, deposition
b. Compaction, cementation, deposition, weathering, erosion
c. Deposition, cementation, compaction, erosion, weathering
d. Weathering, erosion, deposition, compaction, cementation(Correct Answer)
25. Fossils are found only in
a. Intrusive igneous rocks.
b. Extrusive igneous rocks.
c. Sedimentary rocks.(Correct Answer)
d. Metamorphic rocks.
26. What rock-forming process occurs when hot magma comes near and heats up rock?
a. Regional metamorphism
b. Biochemical sedimentation
c. Contact metamorphism(Correct Answer)
d. Deposition
27. A student obtains a cup of quartz sand from a beach. A saltwater solution is poured into the sand and allowed to evaporate. The mineral residue from the saltwater solution cements the sand grains together, forming a material that is most similar to:
a. An extrusive igneous rock.
b. An intrusive igneous rock.
c. A sedimentary rock. (Correct Answer)
d. A metamorphic rock.
28. The most common intrusive igneous rock is
a. Basalt
b. Gabbro
c. Granite(Correct Answer)
d. Pumice
29. True or False: A metamorphic rock that has grains arranged in bands is said to be nonfoliated.
a. True
b. False(Correct Answer)

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