---
title: "Garnet versus granite"
subject: "Engineering Geology I"
chapter: 3
key: "semester_3/engineering_geology_i:garnet-versus-granite"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/garnet-versus-granite
site: BCT Engineering
---

# Garnet versus granite

Engineering Geology I · Chapter 3: Crystallography & Mineralogy

- Asked in: 2063 Baisakh (old course), 2 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/garnet-versus-granite
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-3

## Question

Differentiate between garnet and granite.

## Short answer

Garnet is a single mineral (silicate of Ca, Mg, Fe, Al) with isometric crystals, hardness 6.5–7.5, found in metamorphic rocks, used as abrasive/gem. Granite is a coarse-grained igneous rock composed of quartz, feldspar, mica, hardness ~6–7 overall, used as building stone and aggregate.

## Answer

| Basis | Garnet | Granite |
|---|---|---|
| Nature | A **mineral** (single silicate compound) | A **rock** (aggregate of several minerals) |
| Composition | Silicate of Ca, Mg, Fe, Al (e.g. Fe₃Al₂(SiO₄)₃) | Quartz, feldspar, mica, hornblende |
| Crystal system | Isometric (cubic) | None; a rock is an aggregate of crystals |
| Hardness | 6.5-7.5 | Varies, about 6-7 (as a whole) |
| Origin | Metamorphic rocks mainly (schist, gneiss) | Igneous (intrusive) |
| Colour | Red, brown, green | Pink, grey, white with speckles |
| Texture | Crystal form, dodecahedral | Coarse-grained, granular |
| Use | Abrasive, gem | Building stone, aggregate, foundation |

## Check yourself

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

1. Garnet is a ... and granite is a ...
   A. rock; mineral
   B. rock; rock
   C. mineral; mineral
   D. mineral; rock
   Answer: D. Granite is an aggregate of quartz, feldspar, mica and hornblende. (Key point: Nature)

2. Garnet belongs to the:
   A. Isometric system, while granite has no crystal system
   B. Monoclinic system
   C. Triclinic system
   D. Granite has a hexagonal system
   Answer: A. A rock is a mixture, so it has no single crystal system. (Key point: Crystal system)

3. Granite is generally:
   A. A metamorphic rock
   B. An intrusive igneous rock
   C. A sedimentary rock
   D. A mineral
   Answer: B. Garnet occurs mainly in metamorphic rocks. (Key point: Origin)

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