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

# Hardness versus strength

Engineering Geology I · Chapter 3: Crystallography & Mineralogy

- Asked in: 2062 Baisakh (old course), 2 marks
- Video: [Hardness vs Strength vs Toughness](https://www.youtube.com/watch?v=D_Q-xkwwhMU) — EduTuber
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/hardness-versus-strength
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-3

## Question

Differentiate between hardness and strength.

## Short answer

Hardness is a mineral’s resistance to scratching, measured on the Mohs scale (e.g., quartz 7). Strength is a rock’s ability to resist load without failure, measured in MPa; it depends on mineral type, texture, cementation, and joints. A hard mineral does not ensure a strong rock.

## Answer

| Basis | Hardness | Strength |
|---|---|---|
| Meaning | Resistance to scratching or abrasion | Ability to resist load without failing |
| Applies to | Minerals mainly | Rocks and soils |
| Measurement | Mohs scale (1-10) | Compressive, tensile or shear strength (MPa) |
| Test | Scratch test | Uniaxial compression, point load tests |
| Depends on | Bond strength of minerals | Mineral type, texture, cementation, pores, joints, weathering |
| Nature | Surface property, relative | Bulk property, absolute |
| Example | Quartz = 7 | Granite: about 100-250 MPa |

A hard mineral does not always mean a strong rock; a quartz-rich but weakly cemented sandstone has low strength.

## Check yourself

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

1. Hardness is resistance to:
   A. Load without failing
   B. Dissolving
   C. Scratching or abrasion
   D. Splitting
   Answer: C. Strength is load resistance. (Key point: Hardness meaning)

2. Strength is measured by:
   A. Mohs scale
   B. Streak plate
   C. Acid test
   D. Compressive, tensile or shear tests in MPa
   Answer: D. Hardness is by Mohs scale. (Key point: Strength measurement)

3. A hard mineral does not always mean a strong rock because:
   A. Texture, cementation, pores and joints also control rock strength
   B. Hard minerals are always brittle
   C. Strength depends only on colour
   D. Rocks have no hardness
   Answer: A. Quartz-rich but weakly cemented sandstone is weak. (Key point: Hard but weak)

## Related in Engineering Geology I

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## Related in other subjects

- [Hardness, toughness and strength compared](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Ahardness-toughness-strength-difference) — Civil Engineering Materials, chapter 1
- [Centre of gravity versus centroid](https://www.bctengineer.com/question.md?key=semester_3%2Fstrength_of_materials%3Acentroid-vs-cg) — Strength of Materials, chapter 2