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

Index of Refraction

Gemstone Family

Achorite

3.03 - 3.25

7.0 - 7.5 Mohs

1.610-1.661

Tourmaline

Agate

2.65

7.0 Mohs

1.530 - 1.550

Quartz

Alexandrite

3.68 - 3.78

8.5 Mohs

1.746 - 1.755

Chrysoberyl

Almandine

3.50 - 4.30

6.5 - 7.5 Mohs

1.750 - 1.830

Garnet

Almandine Spinel

3.58 - 4.06

8.0 Mohs

1.708 - 1.735

Spinel

Almandine-Spessartine

3.50 - 4.30

6.5 - 7.5 Mohs

1.750 - 1.830

Garnet

Amazonite

2.55 - 2.76

6.0 - 6.5 Mohs

1.518 - 1.526

Feldspar

Amethyst

2.65

7.0 Mohs

1.532 - 1.554

Quartz

Andradite

3.50 - 4.30

6.5 - 7.5 Mohs

1.880 - 1.940

Garnet

Aquamarine

2.63 - 2.91

7.5 - 8.0 Mohs

1.567-1.590

Beryl

Balas Ruby

3.58 - 4.06

8.0 Mohs

1.708 - 1.735

Spinel

Black Opal

1.98 - 2.25

5.5 - 6.5 Mohs

1.440 - 1.460

Opal

Bloodstone

2.65

7.0 Mohs

1.535 - 1.539

Quartz

Brazilian Emerald

3.03 - 3.25

7.0 - 7.5 Mohs

1.610 - 1.640

Tourmaline

Cairngorm

2.65

7.0 Mohs

1.540 - 1.550

Quartz

Carnelian

2.65

7.0 Mohs

1.530 - 1.550

Quartz

Cat's Eye

3.68 - 3.78

8.5 Mohs

1.746 - 1.755

Chrysoberyl

Chalcedony

2.65

7.0 Mohs

1.544 - 1.553

Quartz

Chlorspinel

3.58 - 4.06

8.0 Mohs

1.712 - 1.717

Spinel

Chrome Pyrope

3.50 - 4.30

6.5 - 7.5 Mohs

1.730 - 1.760

Garnet

Chrysoberyl

3.68 - 3.78

8.5 Mohs

1.746 - 1.755

Chrysoberyl

Chrysoprase

2.65

7.0 Mohs

1.530 - 1.550

Quartz

Citrine

2.65

7.0 Mohs

1.532 - 1.554

Quartz

Color-Change Garnet

3.50 - 4.30

6.5 - 7.5 Mohs

1.730 - 1.760

Garnet

Demantoid

3.50 - 4.30

6.5 - 7.5 Mohs

1.880 - 1.900

Garnet

Diamond

3.51

10 Mohs

2.417

Diamond

Dravite

3.03 - 3.25

7.0 - 7.5 Mohs

1.610-1.661

Tourmaline

Emerald

2.63 - 2.91

7.5 - 8.0 Mohs

1.560 - 1.605

Beryl

Feldspar

2.55 - 2.76

6.0 - 6.5 Mohs

1.518 - 1.572

Feldspar

Fire Opal

1.98 - 2.25

5.5 - 6.5 Mohs

1.430 - 1.460

Opal

Garnet

3.50 - 4.30

6.5 - 7.5 Mohs

1.730 - 1.760

Garnet

Ghanospinel

3.58 - 4.06

8.0 Mohs

1.712 - 1.747

Spinel

Goshenite

2.63 - 2.91

7.5 - 8.0 Mohs

1.570 - 1.600

Beryl

Green Quartz

2.65

7.0 Mohs

1.540-1.550

Quartz

Grossular

3.50 - 4.30

6.5 - 7.5 Mohs

1.880 - 1.940

Garnet

Heliodore

2.63 - 2.91

7.5 - 8.0 Mohs

1.570 - 1.600

Beryl

Heliotrope

2.65

7.0 Mohs

1.535 - 1.539

Quartz

Hessonite

3.50 - 4.30

6.5 - 7.5 Mohs

1.730 - 1.760

Garnet

Hyacinth

4.60 - 4.70

7.5 Mohs

1.777 - 1.987

Zircon

Indicolite

3.03 - 3.25

7.0 - 7.5 Mohs

1.610 - 1.640

Tourmaline

Jade

2.90 - 3.10

6.0 Mohs

1.640 - 1.667

Jade

Jadeite

2.90 - 3.10

6.0 Mohs

1.640 - 1.667

Jade

Jargon

4.60 - 4.70

7.5 Mohs

1.777 - 1.987

Zircon

Jasper

2.65

7.0 Mohs

1.540 - 1.550

Quartz

Labradorite

2.55 - 2.76

6.0 - 6.5 Mohs

1.560 - 1.572

Feldspar

Lapis Lazuli

2.70 - 2.90

5.0 - 5.5 Mohs

1.500 - 1.550

Lapis Lazuli

Malaia

3.50 - 4.30

6.5 - 7.5 Mohs

1.880 - 1.940

Garnet

Matura Diamond

4.60 - 4.70

7.5 Mohs

1.777 - 1.987

Zircon

Moonstone

2.55 - 2.76

6.0 - 6.5 Mohs

1.518 - 1.526

Feldspar

Morganite

2.63 - 2.91

7.5 - 8.0 Mohs

1.585 - 1.594

Beryl

Morion

2.65

7.0 Mohs

1.540 - 1.550

Quartz

Nephrite

2.90 - 3.10

6.0 Mohs

1.600 - 1.641

Jade

Onyx

2.65

7.0 Mohs

1.531 - 1.539

Quartz

Opal

1.98 - 2.25

5.5 - 6.5 Mohs

1.440 - 1.460

Opal

Orthoclase

2.55 - 2.76

6.0 - 6.5 Mohs

1.518 - 1.526

Feldspar

Peridot

3.22 - 3.45

7.0 Mohs

1.635 - 1.690

Peridot

Peristerite

2.55 - 2.76

6.0 - 6.5 Mohs

1.560 - 1.572

Feldspar

Praziolite

2.65

7.0 Mohs

1.540 - 1.550

Quartz

Pyrope

3.50 - 4.30

6.5 - 7.5 Mohs

1.730 - 1.760

Garnet

Pyrope-Almandine

3.50 - 4.30

6.5 - 7.5 Mohs

1.730 - 1.760

Garnet

Pyrope-Spessartine

3.50 - 4.30

6.5 - 7.5 Mohs

1.730 - 1.760

Garnet

Quartz

2.65

7.0 Mohs

1.544 - 1.553

Quartz

Red Beryl

2.63 - 2.91

7.5 - 8.0 Mohs

1.570 - 1.598

Beryl

Rhodolite

3.50 - 4.30

6.5 - 7.5 Mohs

1.740 - 1.770

Garnet

Rock Crystal

2.65

7.0 Mohs

2.000

Quartz

Rose Quartz

2.65

7.0 Mohs

1.540 - 1.550

Quartz

Rubellite

3.03 - 3.25

7.0 - 7.5 Mohs

1.610 - 1.640

Tourmaline

Rubicelle

3.58 - 4.06

8.0 Mohs

1.712 - 1.717

Spinel

Ruby

3.96 - 4.05

9.0 Mohs

1.757 - 1.779

Corundum

Sapphire

3.96 - 4.05

9.0 Mohs

1.757 - 1.779

Corundum

Sapphire Spinel

3.58 - 4.06

8.0 Mohs

1.712 - 1.747

Spinel

Siberite

3.03 - 3.25

7.0 - 7.5 Mohs

1.625-1.675

Tourmaline

Smoky Quartz

2.65

7.0 Mohs

1.540 - 1.550

Quartz

Spessartine

3.50 - 4.30

6.5 - 7.5 Mohs

1.790 - 1.810

Garnet

Spinel

3.58 - 4.06

8.0 Mohs

1.712 - 1.717

Spinel

Sunstone

2.55 - 2.76

6.0 - 6.5 Mohs

1.560 - 1.572

Feldspar

Topaz

3.50 - 3.60

8.0 Mohs

1.607 - 1.627

Topaz

Topazolite

3.50 - 4.30

6.5 - 7.5 Mohs

1.880 - 1.940

Garnet

Tourmaline

3.03 - 3.25

7.0 - 7.5 Mohs

1.603 - 1.655

Tourmaline

Tsavorite

3.50 - 4.30

6.5 - 7.5 Mohs

1.739 - 1.744

Garnet

Turquoise

2.60 - 2.80

5.0 - 6.0 Mohs

1.610 - 1.650

Turquoise

Uvarovite

3.50 - 4.30

6.5 - 7.5 Mohs

1.740 - 1.870

Garnet

Verdilite

3.03 - 3.25

7.0 - 7.5 Mohs

1.612-1.638

Tourmaline

Water Opal

1.98 - 2.25

5.5 - 6.5 Mohs

1.440 - 1.460

Opal

White Opal

1.98 - 2.25

5.5 - 6.5 Mohs

1.440 - 1.460

Opal

Zircon

4.60 - 4.70

7.5 Mohs

1.777 - 1.987

Zircon