Identifying Minerals – Lesson Summary

This is a lesson summary. The full lesson can be viewed by purchasing an online course subscription.

Learning Objective

In this lesson we will learn about some of the physical characteristics of minerals that can be used to identify them.

Learning Outcomes

By the end of this lesson you will be able to:

  • Describe minerals and crystals.
  • Describe examples of crystal shape.
  • Differentiate between cleavage and fracture.
  • Describe Mohs scale of mineral hardness.
  • Describe the streak colour test.
  • Describe examples of mineral lustre.
  • Define specific gravity.

 
identifying minerals online science lesson contents

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Lesson Topics

1 | Properties of Minerals

2 | Crystal Shape

3 | Cleavage and Fracture

4 | Hardness

5 | Colour and Streak

6 | Lustre

7 | Specific Gravity

8 | Summary

Lesson Summary

  • Minerals are naturally occurring solid substances with a defined chemical composition and crystalline structure.
  • Minerals have certain physical properties that can be used to identify them, including: crystal shape, cleavage or fracture, hardness, streak, lustre, and specific gravity.
  • Crystal shapes are divided into six main crystal systems based on their symmetry. These are:
  • Cubic (isometric)
  • Tetragonal
  • Hexagonal and trigonal
  • Orthorhombic
  • Monoclinic
  • Triclinic
  • Cleavage refers to the tendency of a mineral to split along specific planes of weakness, whereas fracture refers to the tendency of a mineral to break in a random manner.
  • Hardness refers to how easily a mineral can be scratched.
  • The Mohs scale of mineral hardness is a reference set of minerals used for classifying the hardness of other minerals.
  • The streak of a mineral is the colour of the powder produced when the mineral is rubbed against a hard, fine-grained surface.
  • Streak is more reliable for identifying minerals than the colour of a mineral itself because it is generally constant, whereas the colour of a mineral can vary due to impurities.
  • Lustre refers to the way a mineral’s surface reflects light.
  • Terms used to describe lustre include: metallic, vitreous, adamantine, pearly, greasy, silky, resinous, waxy, and dull.
  • Specific gravity (relative density) is a measure of density relative to water.
  • Minerals with a higher metal content tend to have higher specific gravities.

 
mohs scale of mineral hardness kit

(Image: Hannes Grobe, Wikimedia Commons)

(Header image: Nikki Zalewski, Adobe Stock)