The Rock Cycle

Igneous, sedimentary, and metamorphic rocks change into one another through weathering, melting, heat, and pressure. Igneous rocks form when magma cools; slow cooling grows larger crystals. Sedimentary rocks show bedding and fossils; metamorphic rocks show foliation from heat and pressure. Follow the process slider through the cycle and compare rock types.

The Rock Cycle

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💡 What is the Rock Cycle?

①Igneous: magma cools and solidifies

②Sedimentary: weathering & erosion → deposition → lithification

③Metamorphic: altered by heat and pressure

④All rocks can transform into each other through the cycle

Rock Types and Textures

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Three Major Rocks

Classification of Rocks

Properties and Uses of Rocks

Rock Comparison

ChartFeatures of Major Rocks

Rock	Type	Features	Uses
Granite	Plutonic	Large crystals, hard	Building / landscape stone
Basalt	Volcanic	Small crystals, dark	Pavement / aggregate
Sandstone	Sedimentary	Sand grains, bedding	Building material
Limestone	Sedimentary	Fizzes with HCl	Cement raw material
Marble	Metamorphic	Metamorphosed limestone	Sculpture / building
Gneiss	Metamorphic	Banded structure	Building foundations

How to Identify Rocks

Igneous = crystals | Sedimentary = bedding/fossils | Metamorphic = banding (foliation)

Each rock type has distinctive features for identification

Exam Key Points

Core Summary

Igneous (cooling) ↔ Sedimentary (weathering) ↔ Metamorphic (heat/pressure) → cycle

The three rock families transform into each other in a cycle

🎯 Exam Key Points

①Igneous: cooled magma (plutonic = large; volcanic = small)

②Sedimentary: bedding, may contain fossils (sandstone, limestone)

③Metamorphic: heat/pressure → foliation (gneiss, marble)

④Limestone + HCl → CO₂ bubbles

⑤Cycle: weathering, melting, heat/pressure transform rocks

Examples and Unit Test

Example 1

Between granite (plutonic) and basalt (volcanic), which has larger crystals (grains), and why?

Igneous rock forms as magma cools, and the more slowly it cools, the larger the crystals grow.

Granite cools slowly deep underground so its crystals are large, while basalt cools quickly at the surface so its crystals are small.

▸ Granite (cools slowly deep underground, so large crystals)

Slow-cooling plutonic rock (granite) has large crystals; fast-cooling volcanic rock (basalt) has small ones.

Example 2

A rock that shows layering (stratification) and a rock that shows banding (foliation) are each what type?

Sedimentary rock forms as grains pile up, so it shows stratification (layers).

Metamorphic rock changes under high heat and pressure, so it shows foliation (banding). So layering = sedimentary, foliation = metamorphic.

▸ Layering = sedimentary / banding (foliation) = metamorphic

Igneous rock is told by crystals, sedimentary by layering, and metamorphic by foliation (banding).

Unit-test style

Which statement about the rock cycle and classification is correct?

①Igneous rock forms from piled-up sand

②Metamorphic rock forms when rock is subjected to heat and pressure

③Basalt cools slowly so it has large crystals

④Sedimentary rock shows foliation (banding)

⑤The three types of rock do not change into one another

▸ ② Metamorphic rock forms when rock is subjected to heat and pressure

Metamorphic rock forms when existing rock changes under high heat and pressure, so ② is correct.

Igneous rock forms from cooled magma (①), basalt cools quickly so its crystals are small (③), sedimentary rock shows layering (④), and the three rocks change into one another and cycle (⑤).

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Use of Minerals and Rocks

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