---
title: "Metamorphic structures"
subject: "Engineering Geology I"
chapter: 4
key: "semester_3/engineering_geology_i:metamorphic-structures"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/metamorphic-structures
site: BCT Engineering
---

# Metamorphic structures

Engineering Geology I · Chapter 4: Petrology

- Asked in: 2076 Asoj, 3 marks
- Video: [ENGINEERING GEOLOGY 2.14 UNIT 2 STRUCTURES & TEXTURES of metamorphic rocks](https://www.youtube.com/watch?v=7aPemOnt6xI) — Dr SUBBARAO GANGISETTY
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/metamorphic-structures
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-4

## Question

Describe the structures of metamorphic rocks.

## Short answer

Metamorphic structures are either foliated, with parallel mineral alignment (slaty cleavage, schistosity, gneissose banding), or non-foliated, including massive granular textures (marble, quartzite) and cataclastic broken fabrics.

## Answer

The structures of metamorphic rocks are of two main kinds.

#### Foliated structures
Parallel arrangement of platy or elongated minerals due to directed pressure.
- **Slaty cleavage** - very fine; the rock splits into thin sheets (slate).
- **Phyllitic structure** - fine, silky sheen, often crinkled (phyllite).
- **Schistose structure** - coarse flaky minerals in parallel layers (schist).
- **Gneissose structure** - alternate light (quartz, feldspar) and dark (mica, hornblende) bands (gneiss).
- **Augen structure** - lens-shaped (eye-shaped) large grains in a foliated matrix (augen gneiss).

#### Non-foliated structures
- **Massive/granulose** - interlocking equigranular grains, no layering (marble, quartzite).
- **Hornfels** - hard, fine grained, dense, from contact metamorphism.
- **Cataclastic** - crushed and broken grains from dynamic metamorphism (mylonite, fault breccia).

## Check yourself

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

1. Which structure shows alternating light and dark bands?
   A. Slaty
   B. Hornfels
   C. Augen
   D. Gneissose
   Answer: D. Quartz-feldspar and mica-hornblende bands. (Key point: Foliated structures)

2. Which are non-foliated structures?
   A. Massive granulose in marble and quartzite, and hornfels
   B. Slaty and phyllitic
   C. Schistose and gneissose
   D. Only cataclastic
   Answer: A. No layered alignment of minerals. (Key point: Non-foliated)

3. Cataclastic structure forms by what?
   A. Contact heating
   B. Dynamic metamorphism crushing grains, as in mylonite
   C. Slow cooling
   D. Deposition
   Answer: B. It occurs near faults. (Key point: Cataclastic)

4. Foliation results from what?
   A. Uniform heat only
   B. Cementation
   C. Directed pressure aligning platy minerals
   D. Volcanic ejection
   Answer: C. Directed stress aligns minerals. (Key point: Foliation cause)

## 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 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
- [Metamorphic rock, cleavage; igneous rock significance](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ametamorphic-rock-cleavage-igneous-rock) — Engineering Geology I, chapter 4