---
title: "Colour versus streak of mineral"
subject: "Engineering Geology I"
chapter: 3
key: "semester_3/engineering_geology_i:colour-versus-streak-of-mineral"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/colour-versus-streak-of-mineral
site: BCT Engineering
---

# Colour versus streak of mineral

Engineering Geology I · Chapter 3: Crystallography & Mineralogy

- Asked in: 2062 Baisakh (old course), 2 marks
- Video: [Mineral identification using Luster, Color, Streak, Hardness and Breakage](https://www.youtube.com/watch?v=i7iF_eY40vo) — Geologia da Terra
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/colour-versus-streak-of-mineral
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-3

## Question

Differentiate between colour and streak of a mineral.

## Short answer

Colour is the bulk appearance in reflected light, variable due to impurities. Streak is the constant powder colour obtained by rubbing on a porcelain plate, reliable for minerals softer than 6.5; e.g., hematite streak is always red-brown regardless of its external colour.

## Answer

| Basis | Colour | Streak |
|---|---|---|
| Meaning | Appearance of the mineral in bulk, in reflected light | Colour of the fine powder of the mineral |
| How observed | By eye on the specimen | By rubbing on unglazed porcelain plate |
| Constancy | Variable; changes with impurities and weathering | Constant for a mineral |
| Reliability | Low | High |
| Applies to | All minerals | Minerals softer than the plate (below 6.5) |
| Example | Hematite may be grey, black or red | Always red-brown streak |
| Quartz | Varied colours | White (colourless) |

## Check yourself

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

1. Which is more reliable for identification?
   A. Colour, as it is constant
   B. Streak, as it is constant
   C. Both equally
   D. Neither
   Answer: B. Colour changes with impurities. (Key point: Reliability)

2. How is streak observed?
   A. By viewing under UV
   B. By scratching glass
   C. By rubbing the mineral on unglazed porcelain
   D. By dropping HCl
   Answer: C. The powder colour appears. (Key point: Streak method)

3. Streak plate works only for minerals:
   A. Harder than 7
   B. All minerals
   C. Metallic only
   D. Softer than the plate (below 6.5)
   Answer: D. Harder minerals scratch the plate instead of leaving powder. (Key point: Limit)

## Related in Engineering Geology I

- [Strike versus streak](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Astrike-versus-streak) — Engineering Geology I, chapter 3, asked 2×

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