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Earth and Space - The Rock Cycle and Types of Rocks

Grade 4IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Rocks are naturally occurring solids made up of one or more minerals, such as Quartz (SiO2SiO_2).

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Igneous Rocks: Formed from the cooling and solidification of molten rock. When it is underground, it is called magma; when it reaches the surface, it is called lava.

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Sedimentary Rocks: Formed from the accumulation of dust, sand, and organic matter. Over millions of years, these layers are pressed together through a process called compactioncompaction and cementationcementation.

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Metamorphic Rocks: Formed when existing igneous or sedimentary rocks are subjected to extreme heat (TT) and pressure (PP), changing their physical and chemical structure.

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The Rock Cycle: A continuous process by which rocks change from one type to another over geological time due to forces like weathering, erosion, and plate tectonics.

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Weathering and Erosion: The breaking down of rocks into smaller pieces (sedimentsediment) by wind, water (H2OH_2O), and ice.

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Fossils: Primarily found in sedimentary rocks because the low-pressure formation process preserves the remains of ancient organisms.

📐Formulae

Sediment+Pressure+Time→SedimentaryRockSediment + Pressure + Time \rightarrow Sedimentary Rock

Magma+Cooling=IgneousRockMagma + Cooling = Igneous Rock

AnyRock+Heat(ΔT)+Pressure(ΔP)→MetamorphicRockAny Rock + Heat (\Delta T) + Pressure (\Delta P) \rightarrow Metamorphic Rock

CaCO3 (Limestone)+Heat/Pressure→MarbleCaCO_3 \text{ (Limestone)} + Heat/Pressure \rightarrow \text{Marble}

SiO2 (Quartz/Sand)+Time→SandstoneSiO_2 \text{ (Quartz/Sand)} + Time \rightarrow \text{Sandstone}

💡Examples

Problem 1:

A scientist finds a rock near a volcano that has large crystals and a grainy texture. What type of rock is it, and how did it form?

Solution:

It is an Intrusive Igneous Rock (e.g., Granite).

Explanation:

Because the rock was near a volcano and has large crystals, it cooled slowly underground from magma. Slow cooling allows larger mineral crystals like Quartz (SiO2SiO_2) and Feldspar to grow.

Problem 2:

If a piece of Limestone (CaCO3CaCO_3) is pushed deep into the Earth's crust where it gets very hot but does not melt, what happens to it?

Solution:

It turns into Marble.

Explanation:

The application of extreme heat (ΔT\Delta T) and pressure (ΔP\Delta P) triggers a metamorphic change, recrystallizing the CaCO3CaCO_3 into a harder, denser rock called Marble.

Problem 3:

Why are fossils rarely found in Igneous rocks?

Solution:

Because of the extreme heat of magma/lava.

Explanation:

Igneous rocks form from molten rock. The temperature (TT) of lava is usually between 700∘C700^\circ C and 1,200∘C1,200^\circ C, which would melt or destroy any organic remains before they could become fossils.