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

# Petrification versus metamorphism

Engineering Geology I · Chapter 4: Petrology

- Asked in: 2059 Chaitra (old course), 4 marks
- Video: [This Is NOT a Tree—Or Is It? (The Petrified Forest Explained)](https://www.youtube.com/watch?v=VmFL5DrtgDE) — Raptor Stories
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/petrification-versus-metamorphism
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-4

## Question

Differentiate between petrification and metamorphism.

## Short answer

Petrification is the replacement of organic matter by minerals to form a fossil, preserving original structure. Metamorphism is the solid-state alteration of pre-existing rocks by heat, pressure, and fluids, forming new rocks like marble.

## Answer

| Point | Petrification | Metamorphism |
|---|---|---|
| Meaning | Conversion of organic remains (wood, shells, bones) into stone by replacement with minerals | Change of an existing rock into a new rock by heat, pressure and fluids in the solid state |
| Material changed | Organic matter such as plants and animals | Igneous, sedimentary or older metamorphic rock |
| Process | Mineral-rich water replaces the organic tissue, molecule by molecule (silica, calcite, pyrite) | Recrystallisation, new minerals, and new textures without melting |
| Agents | Mineral-bearing ground water | Heat, pressure, chemically active fluids |
| Result | Fossil (petrified wood, shell) retaining the original form | New rock (marble, slate, schist) with a new texture and structure |
| Example | Petrified wood | Limestone to marble |

## Check yourself

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

1. Petrification converts what?
   A. Igneous rock to schist
   B. Limestone to marble
   C. Sediment to shale
   D. Organic remains into stone by mineral replacement
   Answer: D. Gives fossils. (Key point: Petrification)

2. Which agent causes petrification?
   A. Mineral-bearing ground water
   B. Heat and pressure
   C. Lava
   D. Glaciers
   Answer: A. Replaces tissue molecule by molecule. (Key point: Agent)

3. Metamorphism acts on what?
   A. Plants
   B. Existing rocks in solid state
   C. Magma
   D. Loose sand only
   Answer: B. No melting. (Key point: Metamorphism)

4. Which pair of examples is correct?
   A. Petrification: limestone to marble; metamorphism: petrified wood
   B. Petrification: shale to slate; metamorphism: petrified shell
   C. Both: petrified wood
   D. Petrification: petrified wood; metamorphism: limestone to marble
   Answer: D. Petrification gives fossils; metamorphism gives new rocks. (Key point: Example)

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