| The relative hardness of solids can be expressed using a scale of numbers from 1 to 10, each relating to a mineral (1 representing Talc and 10 representing Diamond). The method was devised by Frederick Mohs (1773-1839), a German mineralogist. Sets of hardness pencils are use to test specimens to see what will scratchthem; other useful instruments include: Fingernail (2.5), Copper Coin (3.5), Steel Knife (3.5) and Glass (6.0). Below is a list of the properties of common minerals and their Mohs of hardness. |
| Name |
Mohs of Hardness |
Type |
Crystal |
Optical |
| Talc
|
1 |
Silicate |
Monoclinic |
Pale green or grey, pearly lustre. |
| Graphite
| 1-2 |
Trigonal/hexagonal |
Element |
Grey metalic lustre. |
| Gypsum
|
2 |
Monoclinic/trigonal |
Sulphate |
White to transparent. |
| Calcite
|
3 |
Trigonal/hexagonal |
Carbonate |
Double refraction. |
| Barytes
|
3-3.5 |
Orthorhombic |
Sulphate |
Pale, translucent. |
| Aragonite
|
3.5-4 |
Orthorhombic |
Carbonate |
Transulcent white streak. |
| Dolomite
|
3.5-4 |
Trigonal/hexagonal |
Carbonate |
Pale, translucent. |
| Fluorite
|
4 |
Cubic |
Halide |
Many colours, flourescent. |
| Apatite
|
5 |
Trigonal/hexagonal |
Phosphate |
Usually green. |
| Sodalite
|
5.5-6 |
Cubic |
Silicate |
Blue. |
| Pyrite
|
6-6.5 |
Cubic |
Sulphide |
andquot;Fools Goldandquot; |
| Quartz
|
7 |
Trigonal/hexagonal |
Oxide |
Translucent, also microcrystalline. |
| Garnet
|
7 |
Cubic |
Silicate |
Various forms, often plum red. |
| Tourmaline
|
7-7.5 |
Trigonal/hexagonal |
Silicate |
Often pink or green. |
| Zircon
|
7.5 |
Tetragonal |
Silicate |
Often Brown. |
| Beryl
|
7-8 |
Trigonal/hexagonal |
Silicate |
Many colours, emerald green. |
| Spinel
|
7.5-8 |
Cubic |
Oxide |
Many colours, vitreous lustre. |
| Corundum |
9 |
Trigonal/hexagonal |
Oxide |
Various forms including Ruby and Sapphire. |
| Diamond
|
10 |
Cubic |
Element |
Transparent, sparkles if cut. |
