---
title: "Formation of sedimentary and metamorphic rocks"
subject: "Engineering Geology I"
chapter: 4
key: "semester_3/engineering_geology_i:formation-of-sedimentary-and-metamorphic"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/formation-of-sedimentary-and-metamorphic
site: BCT Engineering
---

# Formation of sedimentary and metamorphic rocks

Engineering Geology I · Chapter 4: Petrology

- Asked in: 2059 Chaitra (old course), 4+4 marks
- Video: [The Rock Cycle | Sedimentary, Metamorphic, Igneous | Learning Made Fun](https://www.youtube.com/watch?v=Vp_S3BDiR-I) — Learning Made Fun
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/formation-of-sedimentary-and-metamorphic
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-4

## Question

How are sedimentary and metamorphic rocks formed?

## Short answer

Sedimentary rocks form through weathering, erosion, deposition, compaction, and cementation of sediments. Metamorphic rocks form when existing rocks are changed by heat, pressure, and chemically active fluids without melting, producing new minerals and textures like foliation.

## Answer

#### Formation of sedimentary rocks
Sedimentary rocks form at the Earth's surface.
1. **Weathering** breaks parent rocks into fragments and dissolved ions.
2. **Erosion and transport** by water, wind, ice or gravity.
3. **Deposition** in layers in basins, rivers, lakes and seas. Chemical precipitation and accumulation of organic remains also add material.
4. **Compaction**: weight of upper layers squeezes out water.
5. **Cementation**: silica, calcite or iron oxide binds the grains.
6. **Lithification** completes the change to rock. Examples: sandstone, shale, limestone.

#### Formation of metamorphic rocks
Metamorphic rocks form deep in the crust from existing rocks (igneous, sedimentary or metamorphic) in the solid state under changed conditions.
1. **Heat** (from magma or burial) triggers recrystallisation.
2. **Pressure**: confining pressure compacts the rock; directed stress aligns minerals into foliation.
3. **Chemically active fluids** carry ions and speed up reactions.
4. New minerals (garnet, kyanite, mica) and new textures develop **without melting**.

Types: *contact (thermal) metamorphism* near intrusions (limestone to marble), *regional metamorphism* during mountain building (shale to slate, schist, gneiss) and *dynamic metamorphism* along faults.

Examples: shale to slate to phyllite to schist to gneiss; limestone to marble; sandstone to quartzite.

## Check yourself

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

1. Which comes just before cementation?
   A. Weathering after cementation
   B. Melting
   C. Recrystallisation
   D. Compaction
   Answer: D. Order: weathering, transport, deposition, compaction, cementation, lithification. (Key point: Sedimentary order)

2. How do metamorphic rocks form?
   A. In the solid state, without melting
   B. By melting and cooling
   C. By cementing sediments
   D. By deposition of lava
   Answer: A. New minerals develop without melting. (Key point: Metamorphic without melting)

3. Which is contact metamorphism?
   A. During mountain building, e.g. shale to slate
   B. Near intrusions, e.g. limestone to marble
   C. Along faults, crushing rock
   D. Weathering of granite
   Answer: B. Regional occurs in mountain building. (Key point: Contact vs regional)

4. What sequence shows increasing metamorphic grade?
   A. Gneiss, schist, phyllite, slate, shale
   B. Sandstone, slate, marble
   C. Shale, slate, phyllite, schist, gneiss
   D. Limestone, quartzite, slate
   Answer: C. Grade increases. (Key point: Grade sequence)

## Related in Engineering Geology I

- [Recognising sedimentary, metamorphic, igneous rocks](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Arecognising-sedimentary-metamorphic-igneous-rocks) — 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×
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## Related in other subjects

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