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

# Texture and properties of four rocks

Engineering Geology I · Chapter 4: Petrology

- Asked in: 2079 Bhadra, 4 marks
- 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-and-properties-of-four
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-4

## Question

Describe the texture, structure, mineral composition and engineering properties of quartzite, granite, phyllite and conglomerate.

## Short answer

Quartzite: granoblastic, massive, >90% quartz, strength 150-300 MPa, durable. Granite: holocrystalline, massive, quartz-feldspar-mica, strength 100-250 MPa, low porosity. Phyllite: lepidoblastic, foliated, mica-quartz, weak along foliation, poor for foundations. Conglomerate: rudaceous, bedded, pebbles in matrix, strength depends on cement; siliceous is strong, clayey weak.

## Answer

| Rock | Texture | Structure | Minerals | Engineering properties |
|---|---|---|---|---|
| **Quartzite** (metamorphic) | Granoblastic, interlocking quartz grains | Massive, non-foliated | >90 % quartz | Very hard, strong (150 - 300 MPa), durable; good aggregate and foundation rock; hard to dress |
| **Granite** (igneous, plutonic) | Holocrystalline, phaneritic, granular | Massive, jointed | Quartz, feldspar, mica/hornblende | Strong (100 - 250 MPa), low porosity, durable, takes polish; foundation, dam, building and aggregate use |
| **Phyllite** (metamorphic) | Very fine grained, lepidoblastic, silky sheen | Foliated; phyllitic cleavage, often crinkled | Mica (sericite), chlorite, quartz | Weak along foliation, splits easily, weathers to clay; poor for foundations, tunnels and slopes |
| **Conglomerate** (sedimentary, clastic) | Rudaceous: rounded pebbles/gravel in finer matrix | Bedded, massive, poorly sorted | Pebbles of quartz, quartzite, etc.; cement of silica, calcite or iron oxide | Strength depends on the cement; siliceous cement is strong, clayey is weak; porous, leaks; used as aggregate and for rough walls |

## Check yourself

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

1. Quartzite has
   A. foliation
   B. calcite
   C. granoblastic texture, over 90% quartz, massive
   D. clay cement
   Answer: C. Strong, 150-300 MPa. (Key point: Quartzite)

2. Phyllite is
   A. massive
   B. glassy
   C. coarse
   D. weak along foliation, silky
   Answer: D. Poor for tunnels. (Key point: Phyllite)

3. Conglomerate strength depends on
   A. the cement
   B. foliation
   C. colour
   D. cooling
   Answer: A. Siliceous strong, clayey weak. (Key point: Conglomerate)

4. Granite texture is
   A. lepidoblastic
   B. holocrystalline, phaneritic
   C. rudaceous
   D. glassy
   Answer: B. Plutonic. (Key point: Granite)

## Close variants set in other exams

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

## Related in Engineering Geology I

- [Properties and uses of granite, phyllite, limestone](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aproperties-and-uses-of-granite) — Engineering Geology I, chapter 4, asked 4×
- [Properties of schist, sandstone, phyllite](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aproperties-of-schist-sandstone-phyllite) — 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×
- [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×
- [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

## Related in other subjects

- [Fat lime composition, properties, uses](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Afat-lime-composition-properties-uses) — Civil Engineering Materials, chapter 4