---
title: "Rock cycle"
subject: "Engineering Geology I"
chapter: 4
key: "semester_3/engineering_geology_i:rock-cycle"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/rock-cycle
site: BCT Engineering
---

# Rock cycle

Engineering Geology I · Chapter 4: Petrology

- Asked in: 2081 Bhadra, 3 marks; 2066 Bhadra (old course), 3 marks; 2064 Jestha (old course), 1+3 marks; 2063 Baisakh (old course), 1+1 marks; 2061 Baisakh (old course), 1+3 marks (asked 5 times)
- Video: [The Rock Cycle Explained: How Rocks Form and Change Over Time](https://www.youtube.com/watch?v=uRaVu52eCBQ) — Lessons Made Easy - Teacher Belle
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/rock-cycle
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-4

## Question

What is the rock cycle? Explain how it represents the sequence of formation of the different rock types.

## Short answer

The rock cycle describes continuous transformation among rock types. Igneous rocks form from cooling magma, weather to sediments that lithify into sedimentary rocks, which under heat and pressure become metamorphic rocks; further heating produces magma. Uplift and erosion drive the cycle, with any rock potentially changing into another.

## Answer

The **rock cycle** is the continuous natural process by which rocks of one type are changed into another type through geological processes over millions of years. Any rock may become any other, and no rock is permanent.

```text
            MAGMA <-----------------+
              |                     |
              | cooling             | melting
              v                     |
           IGNEOUS                  |
              | weathering,         |
              | erosion, deposition |
              v                     |
          SEDIMENTS                 |
              | compaction,         |
              | cementation         |
              v                     |
         SEDIMENTARY                |
              | heat, pressure      |
              v                     |
         METAMORPHIC ---------------+
```

#### Sequence
1. **Igneous rocks** form when magma or lava cools and solidifies (granite, basalt).
2. Exposed rocks are broken into fragments by **weathering and erosion**; these are **transported** by water, wind and ice and **deposited** as sediments.
3. Sediments undergo **compaction and cementation** (lithification) into **sedimentary rocks** (sandstone, shale).
4. Under high heat, pressure and chemical fluids, igneous or sedimentary rocks recrystallise to **metamorphic rocks** (gneiss, schist, slate), without melting.
5. If temperature rises further, metamorphic (or any) rocks **melt** into magma, which cools again as igneous rock.

#### Shortcuts
Igneous rocks may be metamorphosed directly; metamorphic and sedimentary rocks may be weathered into new sediments; and uplift brings buried rocks to the surface.

The cycle is driven by the Earth's internal heat and by solar energy through the water cycle.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The rock cycle is:
   A. A continuous process in which rocks change from one type to another over millions of years
   B. A one-way path from sediments to magma
   C. A cycle only of sedimentary rocks
   D. Change in minutes
   Answer: A. No rock is permanent. (Key point: Definition)

2. Metamorphic rocks form when rocks:
   A. Cool from magma
   B. Recrystallise under heat, pressure and fluids without melting
   C. Are cemented from sediments
   D. Melt completely
   Answer: B. Melting gives magma instead. (Key point: Metamorphism)

3. Sediments become sedimentary rock through:
   A. Melting
   B. Foliation
   C. Compaction and cementation
   D. Cooling
   Answer: C. This is lithification. (Key point: Lithification)

4. The cycle is driven by:
   A. Only gravity
   B. Only wind
   C. Human activity
   D. The Earth's internal heat and solar energy via the water cycle
   Answer: D. Internal heat drives melting; solar energy drives weathering. (Key point: Drivers)

## Related in Engineering Geology I

- [Metamorphic rock formation; igneous rock texture](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ametamorphic-rock-formation-igneous-rock) — Engineering Geology I, chapter 4
- [Rock types, rock cycle, sedimentary rock properties](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Arock-types-rock-cycle-sedimentary) — Engineering Geology I, chapter 4
- [Formation of sedimentary rocks](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aformation-of-sedimentary-rocks) — Engineering Geology I, chapter 4, asked 2×

## Related in other subjects

- [One cycle of water hammer pressure wave](https://www.bctengineer.com/question.md?key=semester_4%2Fhydraulics%3Awater-hammer-one-cycle-wave-sketch) — Hydraulics, chapter 4, asked 2×