Jul 20 2008
Mohs Hardness Scale for Minerals
The Mohs hardness scale for minerals is a classification based on scratch-resistance. Basically, the Mohs scale orders minerals from softest (1) to hardest (10), and any mineral with a higher hardness can scratch a mineral with a lower one. Being familiar with this scale is important for a lot of things in mineral collecting. For one thing, when you polish stones in a rock tumbler, you want to make sure that your load contains rocks that are of a similar hardness. Also, you would use different rock tumbler techniques for different hardness levels.
To help sort your stones into similar groups, the following table gives the Mohs hardness scale rating and links to other sources on the stone. We will continue to update this information on a regular basis with more link information and additional stones.
| Mohs Hardness Ranking and Additional Information |
||
|---|---|---|
| Stone | Hardness |
Additional Information |
| Agate | 7 | This link leads to a selection of posts with pictures of various types of agates. |
| Amethyst (Quartz) |
7 | |
| Ametrine (Quartz) |
7 | Here is a photo of an interesting ametrine scepter. |
| Apatite | 5 | |
| Aquamarine | 7.5-8 |
|
| Aventurine | 6.5 |
|
| Azurite | 3.5-4 |
|
| Beryl | 7.5-8 |
|
| Bixbite | 7.5-8 |
|
| Calcite | 3 | |
| Carnelian | 6-7 |
|
| Chrysoberyl | 8.5 |
|
| Chrysocolla | 2.5-3.5 |
|
| Citrine (Quartz) |
7 |
|
| Corundum (Ruby, Sapphire) |
9 | Use boron carbide rather than silicon carbide when polishing. |
| Diamond |
10 |
|
| Fluorite |
4 |
|
| Gypsum | 2 |
|
| Heliodor | 7.5-8 |
|
| Hematite | 5.5-6.5 |
|
| Jade | 6.5-7 |
Grinding stage of polishing in rock tumbler takes longer - up to 2 weeks. |
| Jasper | 6.5-7 |
For some photographs of polished ocean jasper, see this post. |
| Lapis Lazuli |
5-5.5 | |
| Lazulite | 5.5-6 |
|
| Lazurite | 5-5.5 |
|
| Malachite | 3.5-4 |
|
| Moonstone | 6-6.5 |
This link shows a photo of rough moonstone. |
| Morganite | 7.5-8 |
|
| Obsidian | 5-5.5 |
|
| Onyx | 7 |
|
| Orthoclase |
6 |
|
| Peridot | 6.5-7 |
|
| Pyrite | 6-6.8 |
|
| Quartz |
7 |
|
| Ruby (Corundum) |
9 |
Use boron carbide rather than silicon carbide when polishing. |
| Sapphire (Corundum) |
9 |
Use boron carbide rather than silicon carbide when polishing. |
| Sodalite | 5.5-6 | Here’s a picture of some rough spotted sodalite. |
| Sunstone | 6-7.2 |
|
| Talc |
1 |
|
| Tanzanite | 6.5 |
|
| Topaz |
8 |
|
| Tourmaline | 7-7.5 |
|
| Turquoise | 5-6 |
|
This page is still a work in progress. If you have any ideas about something to add, please leave a comment below.
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