1. The Physical Properties of Minerals
GCSE Geology
The Physical Properties of Minerals
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2. The Physical Properties Of Minerals

3. Colour Not particularly useful as a diagnostic property
Some minerals show a wide variety of colours
Quartz can be transparent, white, pink, brown, purple, yellow, orange and even black
Many minerals show very similar colours
Calcite, plagioclase feldspar and halite are commonly grey or white in colour

4. Lustre The way in which minerals reflect light
Glassy, Metallic, Pearly or Dull

5. The mineral reflects light like glass Also known as vitreous lustre
Glassy Lustre
Halite
The mineral reflects light like glass Also known as vitreous lustre

6. Metallic Lustre Galena
Minerals reflect light like metals Metallic lustre often tarnishes to a dull lustre

7. Pearly Lustre The lustre of a pearl or mother of pearl
Shows clearly on the cleavage surfaces of biotite and muscovite mica
Biotite Mica
Muscovite Mica

8. Streak The colour of a mineral’s powder
Obtained by rubbing a mineral specimen on an unglazed white porcelain tile or streak plate
Useful for identifying metallic ore minerals
Silicates generally do not mark the tile and have no streak
White minerals streaked on a white tile will have a white streak
Any minerals harder than the streak plate (6) will scratch it
Haematite gives a red-brown streak

9. Relative Density*
Relative to an equal volume of distilled water at 4 degrees centigrade. 1 litre = 1000g (1kg) 1 cubic centimetre = 1g
Controlled by the atomic weight of the constituent atoms (chemical composition) and the packing (atomic structure)
A useful property for identifying metallic ore minerals, these usually have relative densities over 5.0 and feel particularly dense when hefted in the hand
For example Galena (7.4) Ore of lead and Haematite (5.5) Ore of Iron
Most of the silicate minerals have relative densities between 2.5 and 3.2

10. Measured on Moh’s scale from 1.0 (softest) to 10 (hardest)
Hardness
Measured on Moh’s scale from 1.0 (softest) to 10 (hardest)
Scale was devised by measuring the amount of noise and powder produced from rubbing a mineral on a metal file
Talc 1.0
Diamond 10.0

11. Moh’s Scale of Hardness
10 Diamond
9 Corundum
8 Topaz
7 Quartz
6 Orthoclase Feldspar
Note diamond is over 30 x harder than corundum

12. 5 Apatite 4 Fluorite 3 Calcite 2 Gypsum 1 Talc
Moh’s Scale of Hardness
5 Apatite
4 Fluorite
3 Calcite
2 Gypsum
1 Talc

13. Moh’s Scale of Hardness
Steel nail 5.5
Fingernail 2.5
Copper coin 3.5
Window glass 5.0
Everyday objects can be substituted for minerals on Moh’s scale

14. Testing For Hardness
Try to scratch mineral specimens with substances of known hardness
If a mineral is not scratched by your fingernail, but is scratched by a copper coin then it will have a hardness of between 2.5 and 3.5
If a mineral cannot be scratched by steel it has a hardness of over 5.5
Gypsum is scratched by a fingernail, hardness <2.5

15. The way a mineral breaks when struck by a hammer
Fracture*
The way a mineral breaks when struck by a hammer
The type of fracture is not controlled by any weaknesses in the atomic structure of the mineral

16. Conchoidal Fracture*
This type of fracture is the same as that shown by window glass
A series of concentric curved lines can be seen on the fractured surface
A diagnostic property of the mineral quartz
5mm
Rose quartz showing conchoidal fracture

17. Cleavage The way a mineral breaks when struck by a hammer
Cleavage is controlled by lines of weakness in the atomic structure of the mineral
Minerals can have 1, or 3 planes of cleavage
1 plane, parallel or basal cleavage
2 planes of cleavage that intersect at a characteristic angle
3 planes (cubic, rhombohedral)

18. Minerals showing one plane of cleavage
1cm
Biotite Mica
One plane of cleavage enables the mineral to part along parallel lines. It is like a ream of paper that can be separated into individual sheets.

19. Minerals Showing 2 Sets of Cleavage Planes
1cm
1cm
Augite
Plagioclase Feldspar
Feldspars – intersect at 90 degrees
Augite – intersect at 90 degrees

20. Minerals showing 3 sets of Cleavage Planes
1cm
Produced by the intersection of three cleavage planes
Cubic cleavage 3 planes intersect at 90 degrees e.g. halite
Rhombohedral cleavage 3 planes intersect at 60/120 degrees e.g. calcite
Halite
1cm
Calcite

21. Acid Reaction Use dilute hydrochloric acid to test for carbonates
Calcite effervesces (fizzes) and gives off carbon dioxide gas
Calcite reacting and giving off carbon dioxide
2cm

22. Taste
If a mineral can be tasted in the mouth, then it is soluble in fresh water
Halite (rock salt) tastes salty and is a diagnostic property of the mineral

23. Diagnostic Properties
Properties that allow any mineral to be identified
Most minerals have two or three diagnostic properties
Hardness, cleavage and streak are most useful
Colour, lustre and density are less useful
Special properties such as acid reaction or taste, are often used to identify a mineral
The properties marked with a * are not on the GCSE specification.