UNDERSTANDING
HARDNESS OF GEMSTONES
There
are many systems used to measure hardness, which is defined several
different ways. Gemstones and other minerals are ranked according
to their Mohs hardness. Mohs hardness refers to a material's ability
to resist abrasion or scratching. Note that a hard gem or mineral
is not automatically tough or durable.
About the Mohs scale :
The Moh's (Mohs) scale of hardness is the most common method used
to rank gemstones and minerals according to hardness. Devised by
German mineralogist Friedrich Moh in 1812, this scale grades minerals
on a scale from 1 (very soft) to 10 (very hard). Because the Mohs
scale is a relative scale, the difference between the hardness of
a diamond and that of a ruby is much greater than the difference
in hardness between calcite and gypsum. As an example, diamond (10)
is about 4-5 times harder than corundum (9), which is about 2 times
harder than topaz (8). Individual samples of a mineral may have
slightly different Mohs ratings, but they will be near the same
value. Half-numbers are used for in-between hardness ratings.
How to Use the Mohs Scale :
A mineral with a given hardness rating will scratch other minerals
of the same hardness and all samples with lower hardness ratings.
Gems are examples of minerals. Gold, silver, and platinum are all
relatively soft, with Mohs ratings between 2.5-4. Since gems can
scratch each other and their settings, each piece of gemstone jewelry
should be wrapped separately in silk or paper. Also, be wary of
commercial cleaners, as they may contain abrasives that could damage
jewelry.
Hardness
Mohs
Hardness |
Mineral |
Examples |
1 |
Talc |
--- |
2 |
Gypsum |
--- |
2.5 |
--- |
Fingernail |
3 |
Calcite |
Copper
Penny |
3.5 |
--- |
Adamite |
4 |
Fluorite |
--- |
4.5 |
--- |
Steel
Nail |
5 |
Apatite |
--- |
5.5 |
--- |
Glass |
6 |
Feldspar |
--- |
6.5 |
--- |
Steel
File |
7 |
Quartz |
--- |
7.5 |
--- |
Beryl |
8 |
Topaz |
--- |
9 |
Corundum |
Ruby |
10 |
Diamond |
--- |
Gemstone
Hardness Summary Table
Mohs
Hardness |
Gemstone |
Note |
3.5 |
Azurite
|
|
4.0 |
Malachite |
|
4.0 |
Pearl
|
|
<5 |
Generally
considered too soft for gemstones |
|
5.0 |
Apatite
|
|
5.5 |
Diopside
|
Chrome
Diopside |
5.5 |
Turquoise
|
|
6.0 |
Jade
|
|
6.0 |
Labradorite
|
|
6.0 |
Moonstone |
|
6.0 |
Opal
|
|
6.5 |
Agate
|
|
6.5 |
Kunzite
|
|
6.5 |
Tanzanite
|
|
6.5 |
Onyx |
Chalcedony
|
6.5 |
Peridot
|
|
7.0 |
Amethyst
|
Quartz
|
7.0 |
Citrine |
|
7.0 |
Rose
Quartz |
|
7.0 |
Tiger
Eye |
|
7.0 |
Tourmaline
|
|
7.5 |
Aquamarine |
|
7.5 |
Garnet
|
Tsavorite
|
7.5 |
Zircon |
|
8.0 |
Spinel
|
|
8.0 |
Topaz
|
|
8.5 |
Alexandrite
|
|
8.5 |
Emerald |
Green
beryl |
9.0 |
Ruby
|
|
9.0 |
Sapphire |
|
10.0 |
Diamond
|
|
|
Any
gemstone listed above can be scratched by any gemstone with
the same hardness, or any harder gemstone farther down the
list. |
This
is a fairly comprehensive listing of gemstones with their specific
gravity, Mohs hardness, index of refraction and gemstone family
classification in alphabetical order. We color coated them to help
differentiate between them (these are approximations and subject
to error).
Specific
Gravity :
Specific gravity is the number of times heavier a gemstone of any
volume is than an equal volume of water; in other words, it is the
ratio of the density of the gemstone to the density of water. For
all gemstones listed in this table there is a scientifically determined
specific gravity. You can use the specific gravity and a couple
simple measurements to estimate the carat weight of a stone. We
have created a calculator that makes a gemstone carat weight estimation
using this principle.
Mohs
Hardness :
Hardness can be tested through scratching. A mineral can only be
scratched by a harder substance. Therefore, a relative scale can
be established to account for the differences in hardness simply
by seeing which mineral scratches another. That is exactly what
French mineralogist Friedrich Mohs proposed almost one hundred and
seventy years ago. The Mohs Hardness Scale starting with talc at
1 being the softest and ending with diamond at 10 hardest, is universally
used around the world as a way of distinguishing minerals. Simply
put - the higher the number, the harder the mineral.
Index
of Refraction :
All materials refract light, ie alter its angle. The amount by which
light is refracted is an important feature of every gemstone. The
measure of a material's refractivity is known as its index of refracton
(R.I.). Without going too deeply into physics, light travels at
different speeds through different media. When light passes from
one medium to another, its path is altered (bent) and it is said
to be diffracted.
Gemstone
Family Classification :
The gemstones listed here show every color in the rainbow. Even
with such variety of colors, patterns and shapes - they can be broken
down into 16 different families based on their chemical composition.
|
Gemstone
Name |
Specific
Gravity |
Mohs Hardness |
Achorite |
3.03
- 3.25 |
7.0
- 7.5 Mohs |
Agate |
2.65 |
7.0
Mohs |
Alexandrite |
3.68
- 3.78 |
8.5
Mohs |
Almandine |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Almandine
Spinel |
3.58
- 4.06 |
8.0
Mohs |
Almandine-Spessartine |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Amazonite |
2.55
- 2.76 |
6.0
- 6.5 Mohs |
Amethyst |
2.65 |
7.0
Mohs |
Andradite |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Aquamarine |
2.63
- 2.91 |
7.5
- 8.0 Mohs |
Balas
Ruby |
3.58
- 4.06 |
8.0
Mohs |
Black
Opal |
1.98
- 2.25 |
5.5
- 6.5 Mohs |
Bloodstone |
2.65 |
7.0
Mohs |
Brazilian
Emerald |
3.03
- 3.25 |
7.0
- 7.5 Mohs |
Cairngorm |
2.65 |
7.0
Mohs |
Carnelian |
2.65 |
7.0
Mohs |
Cat's
Eye |
3.68
- 3.78 |
8.5
Mohs |
Chalcedony |
2.65 |
7.0
Mohs |
Chlorspinel |
3.58
- 4.06 |
8.0
Mohs |
Chrome
Pyrope |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Chrysoberyl |
3.68
- 3.78 |
8.5
Mohs |
Chrysoprase |
2.65 |
7.0
Mohs |
Citrine |
2.65 |
7.0
Mohs |
Color-Change
Garnet |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Demantoid |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Diamond |
3.51 |
10
Mohs |
Dravite |
3.03
- 3.25 |
7.0
- 7.5 Mohs |
Emerald |
2.63
- 2.91 |
7.5
- 8.0 Mohs |
Feldspar |
2.55
- 2.76 |
6.0
- 6.5 Mohs |
Fire
Opal |
1.98
- 2.25 |
5.5
- 6.5 Mohs |
Garnet |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Ghanospinel |
3.58
- 4.06 |
8.0
Mohs |
Goshenite |
2.63
- 2.91 |
7.5
- 8.0 Mohs |
Green
Quartz |
2.65 |
7.0
Mohs |
Grossular |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Heliodore |
2.63
- 2.91 |
7.5
- 8.0 Mohs |
Heliotrope |
2.65 |
7.0
Mohs |
Hessonite |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Hyacinth |
4.60
- 4.70 |
7.5
Mohs |
Indicolite |
3.03
- 3.25 |
7.0
- 7.5 Mohs |
Jade |
2.90
- 3.10 |
6.0
Mohs |
Jadeite |
2.90
- 3.10 |
6.0
Mohs |
Jargon |
4.60
- 4.70 |
7.5
Mohs |
Jasper |
2.65 |
7.0
Mohs |
Labradorite |
2.55
- 2.76 |
6.0
- 6.5 Mohs |
Lapis
Lazuli |
2.70
- 2.90 |
5.0
- 5.5 Mohs |
Malaia |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Matura
Diamond |
4.60
- 4.70 |
7.5
Mohs |
Moonstone |
2.55
- 2.76 |
6.0
- 6.5 Mohs |
Morganite |
2.63
- 2.91 |
7.5
- 8.0 Mohs |
Morion |
2.65 |
7.0
Mohs |
Nephrite |
2.90
- 3.10 |
6.0
Mohs |
Onyx |
2.65 |
7.0
Mohs |
Opal |
1.98
- 2.25 |
5.5
- 6.5 Mohs |
Orthoclase |
2.55
- 2.76 |
6.0
- 6.5 Mohs |
Peridot |
3.22
- 3.45 |
7.0
Mohs |
Peristerite |
2.55
- 2.76 |
6.0
- 6.5 Mohs |
Praziolite |
2.65 |
7.0
Mohs |
Pyrope |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Pyrope-Almandine |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Pyrope-Spessartine |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Quartz |
2.65 |
7.0
Mohs |
Red
Beryl |
2.63
- 2.91 |
7.5
- 8.0 Mohs |
Rhodolite |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Rock
Crystal |
2.65 |
7.0
Mohs |
Rose
Quartz |
2.65 |
7.0
Mohs |
Rubellite |
3.03
- 3.25 |
7.0
- 7.5 Mohs |
Rubicelle |
3.58
- 4.06 |
8.0
Mohs |
Ruby |
3.96
- 4.05 |
9.0
Mohs |
Sapphire |
3.96
- 4.05 |
9.0
Mohs |
Sapphire
Spinel |
3.58
- 4.06 |
8.0
Mohs |
Siberite |
3.03
- 3.25 |
7.0
- 7.5 Mohs |
Smoky
Quartz |
2.65 |
7.0
Mohs |
Spessartine |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Spinel |
3.58
- 4.06 |
8.0
Mohs |
Sunstone |
2.55
- 2.76 |
6.0
- 6.5 Mohs |
Topaz |
3.50
- 3.60 |
8.0
Mohs |
Topazolite |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Tourmaline |
3.03
- 3.25 |
7.0
- 7.5 Mohs |
Tsavorite |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Turquoise |
2.60
- 2.80 |
5.0
- 6.0 Mohs |
Uvarovite |
3.50
- 4.30 |
6.5
- 7.5 Mohs |
Verdilite |
3.03
- 3.25 |
7.0
- 7.5 Mohs |
Water
Opal |
1.98
- 2.25 |
5.5
- 6.5 Mohs |
White
Opal |
1.98
- 2.25 |
5.5
- 6.5 Mohs |
Zircon |
4.60
- 4.70 |
7.5
Mohs |
|
Gemstone
Name |
Index
of Refraction |
Gemstone
Family |
Achorite |
1.610-1.661 |
Tourmaline |
Agate |
1.530
- 1.550 |
Quartz |
Alexandrite |
1.746
- 1.755 |
Chrysoberyl |
Almandine |
1.750
- 1.830 |
Garnet |
Almandine
Spinel |
1.708
- 1.735 |
Spinel |
Almandine-Spessartine |
1.750
- 1.830 |
Garnet |
Amazonite |
1.518
- 1.526 |
Feldspar |
Amethyst |
1.532
- 1.554 |
Quartz |
Andradite |
1.880
- 1.940 |
Garnet |
Aquamarine |
1.567-1.590 |
Beryl |
Balas
Ruby |
1.708
- 1.735 |
Spinel |
Black
Opal |
1.440
- 1.460 |
Opal |
Bloodstone |
1.535
- 1.539 |
Quartz |
Brazilian
Emerald |
1.610
- 1.640 |
Tourmaline |
Cairngorm |
1.540
- 1.550 |
Quartz |
Carnelian |
1.530
- 1.550 |
Quartz |
Cat's
Eye |
1.746
- 1.755 |
Chrysoberyl |
Chalcedony |
1.544
- 1.553 |
Quartz |
Chlorspinel |
1.712
- 1.717 |
Spinel |
Chrome
Pyrope |
1.730
- 1.760 |
Garnet |
Chrysoberyl |
1.746
- 1.755 |
Chrysoberyl |
Chrysoprase |
1.530
- 1.550 |
Quartz |
Citrine |
1.532
- 1.554 |
Quartz |
Color-Change
Garnet |
1.730
- 1.760 |
Garnet |
Demantoid |
1.880
- 1.900 |
Garnet |
Diamond |
2.417 |
Diamond |
Dravite |
1.610-1.661 |
Tourmaline |
Emerald |
1.560
- 1.605 |
Beryl |
Feldspar |
1.518
- 1.572 |
Feldspar |
Fire
Opal |
1.430
- 1.460 |
Opal |
Garnet |
1.730
- 1.760 |
Garnet |
Ghanospinel |
1.712
- 1.747 |
Spinel |
Goshenite |
1.570
- 1.600 |
Beryl |
Green
Quartz |
1.540-1.550 |
Quartz |
Grossular |
1.880
- 1.940 |
Garnet |
Heliodore |
1.570
- 1.600 |
Beryl |
Heliotrope |
1.535
- 1.539 |
Quartz |
Hessonite |
1.730
- 1.760 |
Garnet |
Hyacinth |
1.777
- 1.987 |
Zircon |
Indicolite |
1.610
- 1.640 |
Tourmaline |
Jade |
1.640
- 1.667 |
Jade |
Jadeite |
1.640
- 1.667 |
Jade |
Jargon |
1.777
- 1.987 |
Zircon |
Jasper |
1.540
- 1.550 |
Quartz |
Labradorite |
1.560
- 1.572 |
Feldspar |
Lapis
Lazuli |
1.500
- 1.550 |
Lapis
Lazuli |
Malaia |
1.880
- 1.940 |
Garnet |
Matura
Diamond |
1.777
- 1.987 |
Zircon |
Moonstone |
1.518
- 1.526 |
Feldspar |
Morganite |
1.585
- 1.594 |
Beryl |
Morion |
1.540
- 1.550 |
Quartz |
Nephrite |
1.600
- 1.641 |
Jade |
Onyx |
1.531
- 1.539 |
Quartz |
Opal |
1.440
- 1.460 |
Opal |
Orthoclase |
1.518
- 1.526 |
Feldspar |
Peridot |
1.635
- 1.690 |
Peridot |
Peristerite |
1.560
- 1.572 |
Feldspar |
Praziolite |
1.540
- 1.550 |
Quartz |
Pyrope |
1.730
- 1.760 |
Garnet |
Pyrope-Almandine |
1.730
- 1.760 |
Garnet |
Pyrope-Spessartine |
1.730
- 1.760 |
Garnet |
Quartz |
1.544
- 1.553 |
Quartz |
Red
Beryl |
1.570
- 1.598 |
Beryl |
Rhodolite |
1.740
- 1.770 |
Garnet |
Rock
Crystal |
2.000 |
Quartz |
Rose
Quartz |
1.540
- 1.550 |
Quartz |
Rubellite |
1.610
- 1.640 |
Tourmaline |
Rubicelle |
1.712
- 1.717 |
Spinel |
Ruby |
1.757
- 1.779 |
Corundum |
Sapphire |
1.757
- 1.779 |
Corundum |
Sapphire
Spinel |
1.712
- 1.747 |
Spinel |
Siberite |
1.625-1.675 |
Tourmaline |
Smoky
Quartz |
1.540
- 1.550 |
Quartz |
Spessartine |
1.790
- 1.810 |
Garnet |
Spinel |
1.712
- 1.717 |
Spinel |
Sunstone |
1.560
- 1.572 |
Feldspar |
Topaz |
1.607
- 1.627 |
Topaz |
Topazolite |
1.880
- 1.940 |
Garnet |
Tourmaline |
1.603
- 1.655 |
Tourmaline |
Tsavorite |
1.739
- 1.744 |
Garnet |
Turquoise |
1.610
- 1.650 |
Turquoise |
Uvarovite |
1.740
- 1.870 |
Garnet |
Verdilite |
1.612-1.638 |
Tourmaline |
Water
Opal |
1.440
- 1.460 |
Opal |
White
Opal |
1.440
- 1.460 |
Opal |
Zircon |
1.777
- 1.987 |
Zircon |
