Hardness of Gemstones

MOS and Absolute Hardness of most common gemstones used in jewelry design.

The Hardness of Gemstones

This information is not meant as a treatise on the hardness of gemstones, but rather is provided to offer a brief introduction to the topic. Although you may not have been sitting by the computer just hoping for an article on this fascinating topic to pop up on your screen, you might find it both interesting and helpful.

When I began research on this topic, I wondered why jewelry designers should care about the hardness of gemstones. I didn’t have to look far to get the answer. First, hardness is used to help identify unknown gemstones. Wearing my designer hat, this got my attention. I want the vendors from whom I purchase gemstones to know what they are selling and give it the correct label. While I have purchased gemstones from vendors who obviously did not realize they were misrepresenting a stone, it is a pleasure to know that won’t happen at Magpie Gemstones. Several times, I have asked about a stone or strand that I noticed this vendor had set aside and been told that since they cannot be absolutely sure what the stone is they will not sell it.

A second reason to care about the hardness of gemstones applies mainly to those who cut them. Some stones are so soft that they should not be cut for wearable jewelry. Also, knowledge of hardness is important when grinding or polishing gemstones. Do you really want to put that relatively soft gemstone into your tumbler with steel shot? I doubt it!

Now the question follows regarding how hardness is measured in the gemstone business. The hardness of a stone can be measured by how difficult it is to scratch. In 1812, Friedrich Mohs, a German mineralogist, developed the Mohs scale which he based on ten minerals. The Mohs scale is ordinal and merely compares the hardness of one substance to that of another. Later, after the invention of the scale called a sclerometer, mineralogists were able to measure absolute hardness. The chart below includes Mohs ordinal scale as well as the absolute hardness of the ten minerals he measured. Since the invention of the sclerometer, some have reported the finding of materials harder that diamonds which may lead to future changes in this information.

Mohs Scale-Ordinal	Material	Absolute Hardness as Measured by a Sclerometer
1	Talc	1
2	Gypsum	3
3	Calcite	9
4	Fluorite	21
5	Apatite	48
6	Orthoclase	72
7	Quartz	100
8	Topaz	200
9	Corundum	400
10	Diamond	1500

For comparative purposes, let’s look at the chart below showing how Wikopedia references the Mohs scale to everyday objects:

Object	Mohs Scale Hardness
Pencil “lead”	1
Fingernail	2.2-2.5
Copper penny	3.2-3.5
Knife blade	5.5
Window glass	5.5
Steel file	6.5

If you have interest in a particular gemstone you may be able to locate it in the following alphabetical chart, provided by

GemSelect (http://www.gemselect.com/gem-info/gem-hardness-info.php), indicating the Mohs scale for 144 gemstones:

Gem	Hardness
Agate	6.5 - 7
Agate Geode	6.5 - 7
Alexandrite	8.5
Almadine Garnet	6.5 - 7.5
Amazonite	6 - 6.5
Amber	2 - 2.5
Amethyst	7
Ametrine	7
Ammolite	4
Andalusite	7.5
Andesine Labradorite	6 - 6.5
Apatite	5
Aquamarine	7.5 - 8
Aventurine	7
Axinite	6.5 - 7
Azotic Topaz	8
Azurite	3.5 - 4
Beryl	7.5 - 8
Bloodstone	6.5 - 7
Boulder Opal	5.5 - 6.5
Calcite	3
Carnelian	6.5 - 7
Cassiterite	6 - 7
Cat's Eye Apatite	5
Cat's Eye Aquamarine	7.5 - 8
Cat's Eye Diaspore	6.5 - 7
Cat's Eye Scapolite	5.5 - 6
Cat's Eye Tourmaline	7 - 7.5
Chalcedony	6.5 - 7
Charoite	4.5 - 5
Chrome Diopside	5 - 6
Chrome Tourmaline	7 - 7.5
Chrysoberyl	8.5
Chrysoberyl Cat's Eye	8.5
Chrysocolla	2 - 4
Chrysoprase	6.5 - 7
Citrine	7
Clinohumite	6
Color Change Diaspore	6.5 - 7
Color Change Garnet	6.5 - 7.5
Color Change Sapphire	9
Coral	3 - 4
Danburite	7 - 7.5
Demantoid Garnet	7 - 7.5
Dendritic Agate	6.5 - 7
Diamond	10
Dumortierite Quartz	7 - 8.5
Emerald	7.5 - 8
Fire Agate	6.5 - 7
Fire Opal	5.5 - 6.5
Fluorite	4
Fossil Coral	6.5 - 7
Gaspeite	4.5 - 5
Goshenite	7.5 - 8
Grossularite Garnet	6.5 - 7.5
Hackmanite	5.5 - 6
Hambergite	7.5
Hematite	5.5 - 6.5
Hemimorphite	5
Hessonite Garnet	6.5 - 7.5
Hiddenite	6.5 - 7
Idocrase	6.5
Imperial Topaz	8
Iolite	7 - 7.5
Jadeite	6 - 6.5
Jasper	6.5 - 7
Kunzite	7
Kyanite	6 - 7
Labradorite	6 - 6.5
Lapis Lazuli	5 - 6
Larimar	4.5 - 5
Lepidolite	2.5 - 3
Malachite	3.5 - 4
Mali Garnet	6.5 - 7.5
Maw-Sit-Sit	6 - 7
Melanite	6.5 - 7
Moldavite	5.5
Moonstone	6 - 6.5
Morganite	7.5 - 8
Moss Opal	5.5 - 6.5
Mystic Quartz	7
Mystic Topaz	8
Nephrite Jade	6 - 6.5
Nuumite	5.5 - 6
Obsidian	5 - 5.5
Onyx	6.5 - 7
Opal	5.5 - 6.5
Opal Doublet	5.5 - 6.5
Orthoclase	6 - 6.5
Paraiba Tourmaline	7 - 7.5
Peanut Wood	6.5 - 7
Pearl	2.5 - 4.5
Peridot	6.5 - 7
Prehnite	6 - 6.5
Pyrope Garnet	6.5 - 7.5
Quartz	7
Quartz Cat's Eye	7
Rainbow Moonstone	6 - 6.5
Rainbow Pyrite	6 - 6.5
Rhodochrosite	4
Rhodolite Garnet	6.5 - 7.5
Rhodonite	5.5 - 6.5
Rose Quartz	7
Rubellite Tourmaline	7 - 7.5
Ruby	9
Ruby-Zoisite	6.5 - 7
Rutile Quartz	7
Rutile Topaz	8
Sapphire	9
Scapolite	5.5 - 6
Seraphinite	2 - 4
Sillimanite Cat's Eye	6.5 - 7.5
Smithsonite	5
Smoky Quartz	7
Snowflake Obsidian	5 - 5.5
Sodalite	5.5 - 6
Spessartite Garnet	6.5 - 7.5
Sphalerite	3.5 - 4
Sphene	5 - 5.5
Spinel	8
Spodumene	6.5 - 7
Star Diopside	5 - 6
Star Garnet	6.5 - 7.5
Star Lemon Quartz	7
Star Moonstone	6 - 6.5
Star Rose Quartz	6.5 - 7
Star Ruby	9
Star Sapphire	9
Star Sunstone	6 - 6.5
Strawberry Quartz	7
Sugilite	6 - 6.5
Sunstone	6 - 6.5
Tanzanite	6.5 - 7
Tashmarine Diopside	5 - 6
Tiger's Eye	6.5 - 7
Tiger's Eye Matrix	6.5 - 7
Topaz	8
Tourmaline	7 - 7.5
Tremolite-Hexagonite	5 - 6
Tsavorite Garnet	6.5 - 7.5
Turquoise	5 - 6
Variscite	4 - 5
Verdite	3
Zircon	6.5 - 7.5

Now you know more than you probably wanted to know about the hardness of gemstones. I hope that your friends and customers will be impressed by your new knowledge.

Dr Karen Meador compiled this article and charts for us and for that we are eternally grateful.

Karen Meador

**Contributing authors are noted in the articles they wrote. All articles are copyright. You can reprint these articles as long as the original author is sited and a link to this website is included. The name Magpie Gemstones must be used as the hypertext.

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