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Moh's Hardness Scale
In 1822, a German Mineralogist, Friedrich Moh, developed a hardness
scale. While not scientifically based on the true numerical hardness
of gemstones, it is so practical in its application, it's still
in use today by most Geologists and Gemologists.
Some things should be said first--some stones/gems
are harder in one direction than the other. For instance, Calcite
is easily scratched with a nail in one direction (Hardness 2), but
difficult to scratch in another direction (Hardness 3).
Some handy points of reference are: a fingernail,
about 2 -2 1/2. A copper penny is about a Hardness of 3, a steel
knife, a bit over 5 and glass about 5 1/2. Really good steel runs
about 6 1/2.
| Moh's Hardness Scale |
| Stone Name |
|
Hardness |
| ALEXANDRITE |
-
|
8.5 |
| AMBER |
- |
2.0-3.0 |
| AMETHYST |
- |
7.0 |
| AMETRINE |
- |
7.0 |
| ANDALUZITE |
- |
7.0-7.5 |
| APATITE |
- |
5.0 |
| AQUAMARINE |
- |
7.5-8.0 |
| BERYL |
- |
7.5-8.0 |
| CALCITE |
- |
3.0 |
| CHALCEDONY |
- |
7.0 |
| CHRYSOBERYL |
- |
8.5 |
| CHRYSOPHRASE |
- |
6.5-7.0 |
| CITRINE |
- |
7.0 |
| DANBURITE |
- |
7.0 |
| DIOPSIDE |
- |
5.5-6.0 |
| EMERALD |
- |
7.5-8.0 |
| ENSTATITE |
- |
5.0-6.0 |
| FLUORITE |
- |
4.0-4.5 |
| GARNET |
- |
7.0-7.5 |
| IOLITE |
- |
7.0-7.5 |
| JADEITE |
- |
6.5-7.0 |
| KORNERUPINE |
- |
6.5-7.0 |
| KUNZITE |
- |
6.0-7.0 |
| KYANITE |
- |
4.0-7.5 |
| LABRODORITE |
- |
6.0-6.5 |
| MALACHITE |
- |
3.5-4.0 |
| MORGANITE |
- |
7.5-8.0 |
| MOON STONE |
- |
6.0-6.5 |
| NEPHRITE |
- |
6.0-6.5 |
| OPAL |
- |
5.5-6.5 |
| PADPARADSCHA |
- |
9.0 |
| PEARL |
- |
3.0-4.0 |
| PERIDOT |
- |
6.5-7.0 |
| PRASIOLITE |
- |
7.0 |
| QUARTZ |
- |
7.0 |
| RHODOCHROSITE |
- |
4.0 |
| RHODOLITE |
- |
7.0-7.5 |
| ROSE QUARTZ |
- |
7.0 |
| RUBY |
- |
9.0 |
| RUBELLITE |
- |
7.0-7.5 |
| RUTELLITE |
- |
7.0 |
| SAPPHIRE |
- |
9.0 |
| SCAPOLITE |
- |
6.0-6.5 |
| SILLIMINITE (FIBROLITE) |
- |
6.0-7.5 |
| SINHALITE |
- |
6.5 |
| SPESSARTITE |
- |
7.0-7.5 |
| SPHALERITE |
- |
3.5-4.0 |
| SPHENE |
- |
5.0-5.5 |
| SPINEL |
- |
8.0 |
| STAR RUBY |
- |
9.0 |
| SUN STONE |
- |
6.0-6.5 |
| TSAVORITE |
- |
7.0-7.5 |
| TANZANITE |
- |
6.5-7.0 |
| TOURMALINE |
- |
7.0-7.5 |
| TOPAZ |
- |
8.0 |
| ZIRCON |
- |
6.0-7.5 |
| Hardness Description |
| Hardness |
Key Stone |
Comments |
| 10 |
Diamond |
Hardest mineral known to man |
| 9 |
Corundum
(Sapphire/Ruby) |
Harder than Topaz |
| 8 |
Topaz |
Harder than Quartz |
| 7 |
Quartz |
Scratches Glass |
| 6 |
Microcline |
Suitable for gems |
| 5 |
Apatite |
About the hardness of teeth |
| 4 |
Fluorite |
Cannot be scratched with a nail |
| 3 |
Calcite |
Difficult to scratch with a nail |
| 2 |
Gypsum |
Easily scratched with nail |
| 1 |
Talc |
Very soft, chalk-like |
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