---
title: "Agents of metamorphism"
subject: "Engineering Geology I"
chapter: 4
key: "semester_3/engineering_geology_i:agents-of-metamorphism"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/agents-of-metamorphism
site: BCT Engineering
---

# Agents of metamorphism

Engineering Geology I · Chapter 4: Petrology

- Asked in: 2076 Chaitra, 2 marks; 2076 Asoj, 1 marks (asked 2 times)
- Video: [Agents and Types of Metamorphism - Mineralogy and Petrology - Engineering Geology](https://www.youtube.com/watch?v=n05o_0Tg5Ew) — 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/agents-of-metamorphism
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-4

## Question

Enumerate the various agents (factors) of metamorphism and explain their role.

## Short answer

The main agents are heat (provides energy for recrystallization), pressure (confining pressure densifies rocks, directed stress causes foliation), and chemically active fluids (speed up reactions and enable metasomatism). Time allows well‑formed minerals.

## Answer

**Metamorphism** is the change in mineral composition, texture and structure of a rock in the solid state, due to changes in temperature, pressure and chemical environment.

#### Agents (factors) of metamorphism
**1. Heat (temperature)**
- Source: magma intrusion, deep burial (geothermal gradient), friction on faults.
- Role: provides energy for chemical reactions, causing recrystallisation and growth of new minerals (e.g. limestone to marble, shale to hornfels). Range roughly 200-800 °C.

**2. Pressure**
- *Confining (lithostatic) pressure*: from the weight of overlying rocks; acts equally in all directions, makes rocks denser and forms minerals with compact structure.
- *Directed (differential) stress*: from plate movements; flattens and aligns minerals, giving foliation, slaty cleavage and schistosity.

**3. Chemically active fluids**
- Water and gases (CO₂, H₂O, fluorine) carry ions to and from the rock.
- Role: speed up reactions and introduce new materials (metasomatism).

**Time** also matters: slow, long action gives well-formed minerals.

## Check yourself

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

1. Which are the agents of metamorphism?
   A. Wind, water and ice
   B. Weathering, erosion and deposition
   C. Heat, pressure and chemically active fluids
   D. Melting, cooling and crystallisation
   Answer: C. Time also matters. (Key point: Agents)

2. What does directed (differential) stress produce?
   A. Denser rocks with equal pressure in all directions
   B. Melting of the rock
   C. Glassy texture
   D. Flattening and alignment of minerals, giving foliation
   Answer: D. Confining pressure densifies; directed stress aligns. (Key point: Directed stress)

3. What is metasomatism?
   A. Introduction of new material by fluids
   B. Melting of rock by heat
   C. Cementation of sediment
   D. Rapid cooling of lava
   Answer: A. Chemically active fluids carry ions in and out and speed reactions. (Key point: Fluids)

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