NGS Rocks & Minerals Section 3: Classifying Rocks

What are the three major groups of rocks?

• Metamorphic, Igneous, Volcanic

• Sedimentary, Metamorphic, Volcanic

• Igneous, Volcanic, Sedimentary

• Igneous, Sedimentary, Metamorphic

Answer explanation

The three major groups of rocks are:

• Igneous: Formed from the cooling and solidification of molten rock (magma or lava).

• Sedimentary: Formed from the accumulation and cementation of sediments, such as sand, mud, and organic debris.

• Metamorphic: Formed when existing rocks are subjected to extreme heat and pressure, causing them to change in texture and mineral composition.

Therefore, the correct answer is:

• Igneous, Sedimentary, Metamorphic

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How are igneous rocks formed?

• By erosion and sedimentation

• By cooling and crystallization of magma or lava

• By heat and pressure

• By chemical reactions

Answer explanation

Igneous rocks are formed by:

• Cooling and crystallization of magma or lava:

  • Imagine super-hot melted rock deep inside the Earth. This melted rock is called magma.

  • When magma rises towards the surface or erupts from a volcano as lava, it starts to cool down.

  • As it cools, the melted rock begins to solidify and form crystals.

  • The size and type of crystals depend on how quickly the magma or lava cools.

Therefore, the correct answer is:

• By cooling and crystallization of magma or lava

• How igneous rocks are formed. Credit: Wikipedia Commons/Jasmin Ros

Tags

NGSS.HS-ESS2-3

Which rock is light-colored with high silica content?

• Granite

• Basalt

• Slate

• Limestone

Answer explanation

The rock that is light-colored with high silica content is Granite.

• Granite is a common type of igneous rock that is typically light-colored, often with shades of pink, gray, or white.

• It is rich in silica (silicon dioxide), which contributes to its light color and hardness.

Image credit - James St. John, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons

What is the process called when sediment solidifies into rock?

• Erosion

• Crystallization

• Metamorphism

• Lithification

Answer explanation

The process when sediment solidifies into rock is called Lithification.

• Lithification involves two main processes:

  • Compaction: Overlying sediments exert pressure on deeper layers, squeezing them together and reducing the space between particles.

  • Cementation: Minerals dissolved in water (like silica or calcite) precipitate and fill the spaces between sediment grains, acting like a glue to bind them together.

• Image Credit : Carie Frantz (Carie027), CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

What is the main factor in classifying rocks?

• How the rock formed

• The rock's age

• The rock's location

• The rock's size

Answer explanation

The main factor in classifying rocks is how the rock formed.

• This is because the formation process (igneous, sedimentary, or metamorphic) directly determines the rock's mineral composition, texture, and overall characteristics.

• This image visually represents how rocks are constantly changing and transforming through the processes of:

  • Igneous Rock Formation: Cooling and solidification of magma or lava.  

  • Sedimentary Rock Formation: Weathering, erosion, deposition, and lithification of sediments.  

  • Metamorphic Rock Formation: Existing rocks undergoing intense heat and pressure.

• Attribution:
  

  Fabio Crameri, CC BY-SA 4.0, via Wikimedia Commons

What are rock-forming minerals?

• Twenty minerals that make up most of Earth's crust

• Minerals that are found in sedimentary rocks

• Minerals found only in igneous rocks

• Minerals that form only under high pressure

Answer explanation

The correct answer is:

• Twenty minerals that make up most of Earth's crust

Rock-forming minerals are the most common minerals found in the Earth's crust. They are the building blocks of most rocks.

Some of the most common rock-forming minerals include:

• Feldspar: A group of silicate minerals that are the most abundant minerals in the Earth's crust.

• Quartz: A hard, crystalline mineral composed of silicon and oxygen.

• Mica: A group of silicate minerals known for their sheet-like structure.

• Pyroxene: A group of silicate minerals commonly found in igneous rocks.

• Amphibole: A group of silicate minerals often found in metamorphic rocks.

How do sedimentary rocks form?

• From chemical reactions

• From broken pieces of rocks or dissolved minerals

• From cooling magma

• From volcanic eruptions

Answer explanation

Sedimentary rocks form from broken pieces of rocks or dissolved minerals. These pieces, called sediments, can come from a variety of sources, including:  

• Weathering of existing rocks: Wind, water, and ice can break down rocks into smaller pieces.  

• Erosion: These broken pieces are then transported by wind, water, or ice and deposited in new locations.  

• Deposition: The sediments settle and accumulate in layers.  

• Compaction: Over time, the weight of the overlying layers compresses the sediments, squeezing out water and air.  

• Cementation: Minerals dissolved in water precipitate and fill the spaces between the sediment grains, binding them together to form solid rock.  

Here are some examples of sedimentary rocks:

• Sandstone: Formed from sand grains cemented together.  

• Shale: Formed from compacted clay.  

• Limestone: Formed from the shells and skeletons of marine organisms.

Tags

NGSS.MS-ESS2-1

What is the rock cycle?

• A series of processes that change one type of rock into another

• The process of rocks melting into magma

• The cycle of erosion and weathering

• The formation of mountains

Tags

NGSS.MS-ESS2-1

What is the texture of a rock?

• The weight of the rock

• The size of the rock

• The color of the rock

• The look and feel of the rock's surface

Answer explanation

The rock cycle is a continuous process where rocks are constantly being formed, broken down, and transformed into different types.  

Here's a simple breakdown:

• Igneous rocks form from the cooling and solidification of molten rock (magma or lava).  

• Sedimentary rocks form from the accumulation and cementation of sediments (like sand, mud, and organic matter).  

• Metamorphic rocks form when existing rocks are subjected to extreme heat and pressure, causing them to change in texture and mineral composition.  

These processes are interconnected, and rocks can transition from one type to another over long periods of time.

Attribution:

Fabio Crameri, CC BY-SA 4.0, via Wikimedia Commons

How do metamorphic rocks form?

• By erosion and sedimentation

• By cooling and crystallization

• By volcanic eruptions

• By heat, pressure, or chemical reactions