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

# Formation of sedimentary rocks

Engineering Geology I · Chapter 4: Petrology

- Asked in: 2066 Bhadra (old course), 2 marks; 2068 Baisakh, 2 marks (asked 2 times)
- Video: [Sedimentary Rocks](https://www.youtube.com/watch?v=uozyWZ6XQzM) — GeoScience Videos
- 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-rocks
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-4

## Question

How is sedimentary rock formed?

## Short answer

Sedimentary rocks form by weathering, erosion, transportation, and deposition of particles in layers, followed by compaction from overburden and cementation by minerals like silica or calcite. This lithification (diagenesis) turns loose sediments into solid rocks like sandstone and shale.

## Answer

Sedimentary rocks form at the Earth's surface by the accumulation and hardening of sediments, in these stages.

1. **Weathering** (physical, chemical) breaks existing rocks into fragments and dissolved material.
2. **Erosion and transportation** by water, wind, ice or gravity carry the particles away. Particles get rounded and sorted by size.
3. **Deposition** occurs in lakes, rivers, seas and deserts when the energy of the transporting agent falls, forming horizontal layers (strata). Chemical and organic matter also precipitate or accumulate.
4. **Compaction**: the weight of overlying sediments squeezes out water and reduces pore space.
5. **Cementation**: minerals such as silica, calcite and iron oxide precipitate from water and bind the grains.
6. **Lithification**: the loose sediments become solid rock (**diagenesis**).

Result: layered rocks such as sandstone, shale and limestone, with fossils and structures like ripple marks.

## Check yourself

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

1. What is the correct order of sedimentary rock formation?
   A. Deposition, weathering, cementation, transport
   B. Weathering, transport, deposition, compaction, cementation
   C. Melting, cooling, crystallisation, cementation
   D. Compaction, weathering, transport, melting
   Answer: B. Sediments are produced, moved, laid down, squeezed and cemented. (Key point: Order of stages)

2. What does compaction do?
   A. It precipitates silica between grains
   B. It melts the grains together
   C. The weight of overlying sediments squeezes out water and reduces pore space
   D. It breaks rock into fragments
   Answer: C. Compaction is by overburden weight; cementation binds grains. (Key point: Compaction)

3. Which minerals commonly act as cement?
   A. Garnet, kyanite and talc
   B. Olivine and pyroxene
   C. Mica and chlorite only
   D. Silica, calcite and iron oxide
   Answer: D. These precipitate from water and bind the grains. (Key point: Cementation)

## Related in Engineering Geology I

- [Formation of sedimentary and metamorphic rocks](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aformation-of-sedimentary-and-metamorphic) — Engineering Geology I, chapter 4
- [Texture of sedimentary rocks and rock cleavage](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Atexture-of-sedimentary-rocks-and) — 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
- [Classification of sedimentary rocks](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aclassification-of-sedimentary-rocks) — Engineering Geology I, chapter 4, asked 4×
- [Texture of sedimentary rocks](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Atexture-of-sedimentary-rocks) — Engineering Geology I, chapter 4, asked 2×
- [Identify sedimentary rocks in the field](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aidentify-sedimentary-rocks-in-the) — Engineering Geology I, chapter 4

## Related in other subjects

- [How soils are formed](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Asoil-formation-process) — Soil Mechanics, chapter 1, asked 2×