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

# Texture of sedimentary rocks

Engineering Geology I · Chapter 4: Petrology

- Asked in: 2072 Chaitra, 2 marks; 2068 Baisakh, 4 marks (asked 2 times)
- Video: [Texture of Sedimentary Rocks](https://www.youtube.com/watch?v=2rjEkrVVkd0) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/texture-of-sedimentary-rocks
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-4

## Question

Describe the texture of sedimentary rocks.

## Short answer

Sedimentary textures are clastic (cemented grains described by size, shape, sorting, packing, and cement) or non-clastic (crystalline, oolitic, bioclastic, or amorphous). Grain size, sorting, and cement control rock strength and porosity.

## Answer

**Texture** is the size, shape and arrangement of grains and their relationship in a rock. Sedimentary textures are of two main types.

#### 1. Clastic (fragmental) texture
Rock is made up of broken grains cemented together. Features:
- **Grain size**: gravel (> 2 mm), sand (2 to 1/16 mm), silt and clay (< 1/16 mm).
- **Grain shape**: angular (little transport, breccia) to rounded (long transport, conglomerate); sphericity.
- **Sorting**: well sorted (similar size) or poorly sorted (mixed sizes).
- **Packing** and **fabric**: arrangement of grains and pore space.
- **Cement and matrix**: silica, calcite or iron oxide cement; fine matrix between grains.

#### 2. Non-clastic texture
- **Crystalline**: interlocking crystals from chemical precipitation (rock salt, gypsum, chemical limestone).
- **Oolitic**: small spherical grains (ooliths) in limestone.
- **Bioclastic / organic**: shell fragments, fossils (coquina, coral limestone).
- **Amorphous** or **cryptocrystalline**: chert.

The grain size, sorting and cement control the strength and porosity of the rock.

## Check yourself

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

1. Sedimentary textures are of which two main types?
   A. Clastic and non-clastic
   B. Phaneritic and aphanitic
   C. Foliated and massive
   D. Holocrystalline and holohyaline
   Answer: A. Clastic means fragmental; non-clastic includes crystalline, oolitic and bioclastic. (Key point: Two textures)

2. What does a rock of angular grains indicate?
   A. Long transport, as in conglomerate
   B. Little transport, as in breccia
   C. Chemical precipitation
   D. Rapid cooling
   Answer: B. Rounded grains mean long transport; angular grains mean short. (Key point: Grain shape)

3. Oolitic texture means
   A. shell fragments
   B. wholly glassy matter
   C. small spherical grains (ooliths), as in limestone
   D. interlocking quartz and feldspar
   Answer: C. Ooliths are tiny spheres in limestone; shell fragments are bioclastic. (Key point: Oolitic)

4. Which factors control the strength and porosity of a sedimentary rock?
   A. Only colour
   B. Only the age
   C. The rate of magma cooling
   D. Grain size, sorting and cement
   Answer: D. The answer says grain size, sorting and cement control strength and porosity. (Key point: Control of strength)

## Related in Engineering Geology I

- [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
- [Texture of igneous rocks](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Atexture-of-igneous-rocks) — Engineering Geology I, chapter 4, asked 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×
- [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
- [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 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