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Gemstone Hardness

The Mohs scale of mineral hardness was created by German mineralogist, Friedrich Mohs, in 1822 to measure the relative hardness or scratch resistance of various minerals. He based it on ten readily available minerals. As it is an ordinal scale, two minerals must be compared to decide which is harder. The scale is neither linear nor logarithmic. For example, corundum is twice as hard as topaz, but diamond is almost four times as hard as corundum.

Diamond Has a Mohs Hardness of 10
Diamond - The Hardest Gemstone

The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, or the softest material that can scratch the given material.

Mohs' original scale of mineral hardness is as follows:

Hardness Material Absolute Hardness
1 Talc (Mg3Si4O10(OH)2) 1
2 Gypsum (CaSO4·2H2O) 3
3 Calcite (CaCO3) 9
4 Fluorite (CaF2) 21
5 Apatite (Ca5(PO4)3(OH-,Cl-,F-)) 48
6 Orthoclase (KAlSi3O8) 72
7 Quartz (SiO2) 100
8 Topaz (Al2SiO4(OH-,F-)2) 200
9 Corundum (Al2O3) 400
10 Diamond (C) 1500

To give some examples from everyday life,
a fingernail has a hardness of 2;
a copper penny, about 3;
a knife blade, 5;
window glass, 5.5;
and a steel file, 6.5.

Here are the Mohs scale ratings for 144 types of gemstones:

Gem Hardness Info Page
Diamond 10 Diamond Information Page
Ruby 9 Ruby Information Page
Sapphire 9 Sapphire Information Page
Star Ruby 9 Star Ruby Information Page
Star Sapphire 9 Star Sapphire Information Page
Color-Change Sapphire 9 Color Change Sapphire Information Page
Chrysoberyl Cat's Eye 8.5 Chrysoberyl Cat's Eye Information Page
Alexandrite 8.5 Alexandrite Information Page
Chrysoberyl 8.5 Chrysoberyl Information Page
Topaz 8 Topaz Information Page
Rutile Topaz 8 Rutile Topaz Information Page
Azotic Topaz 8 Azotic Topaz Information Page
Mystic Topaz 8 Mystic Topaz Information Page
Spinel 8 Spinel Information Page
Imperial Topaz 8 Imperial Topaz Information Page
Emerald 7.5 - 8 Emerald Information Page
Andalusite 7.5 Andalusite Information Page
Hambergite 7.5 Hambergite Information Page
Aquamarine 7.5 - 8 Aquamarine Information Page
Goshenite 7.5 - 8 Goshenite Information Page
Cat's Eye Aquamarine 7.5 - 8 Cat's Eye Aquamarine Information Page
Beryl 7.5 - 8 Beryl Information Page
Morganite 7.5 - 8 Morganite Information Page
Demantoid Garnet 7 - 7.5 Demantoid Garnet Information Page
Quartz Cat's Eye 7 Quartz Information Page
Amethyst 7 Amethyst Information Page
Cat's Eye Tourmaline 7 - 7.5 Cat's Eye Tourmaline Information Page
Smoky Quartz 7 Quartz Information Page
Quartz 7 Quartz Information Page
Tourmaline 7 - 7.5 Tourmaline Information Page
Star Lemon Quartz 7 Quartz Information Page
Rose Quartz 7 Rose Quartz Information Page
Ametrine 7 Ametrine Information Page
Kunzite 7 Kunzite Information Page
Citrine 7 Citrine Information Page
Mystic Quartz 7 Mystic Quartz Information Page
Paraiba Tourmaline 7 - 7.5 Paraiba Tourmaline Information Page
Danburite 7 - 7.5 Danburite Information Page
Strawberry Quartz 7 Strawberry Quartz Information Page
Aventurine 7 Aventurine Information Page
Rutile Quartz 7 Rutile Quartz Information Page
Chrome Tourmaline 7 - 7.5 Tourmaline Information Page
Dumortierite Quartz 7 - 8.5 Dumortierite Quartz Information Page
Iolite 7 - 7.5 Iolite Information Page
Rubellite Tourmaline 7 - 7.5 Rubellite Tourmaline Information Page
Tanzanite 6.5 - 7 Tanzanite Information Page
Peridot 6.5 - 7 Peridot Information Page
Mali Garnet 6.5 - 7.5 Mali Garnet Information Page
Jasper 6.5 - 7 Jasper Information Page
Axinite 6.5 - 7 Axinite Information Page
Chrysoprase 6.5 - 7 Chrysoprase Information Page
Fossil Coral 6.5 - 7 Fossil Coral Information Page
Dendritic Agate 6.5 - 7 Dendritic Agate Information Page
Spessartite Garnet 6.5 - 7.5 Spessartite Garnet Information Page
Fire Agate 6.5 - 7 Fire Agate Information Page
Tiger's Eye 6.5 - 7 Tiger's Eye Information Page
Grossularite Garnet 6.5 - 7.5 Grossularite Information Page
Agate Geode 6.5 - 7 Agate Geode Information Page
Star Rose Quartz 6.5 - 7 Rose Quartz Information Page
Ruby-Zoisite 6.5 - 7 Ruby Zoisite Information Page
Star Garnet 6.5 - 7.5 Garnet Information Page
Idocrase 6.5 Idocrase Information Page
Color-Change Garnet 6.5 - 7.5 Garnet Information Page
Hiddenite 6.5 - 7 Hiddenite Information Page
Agate 6.5 - 7 Agate Information Page
Melanite 6.5 - 7 Melanite Information Page
Zircon 6.5 - 7.5 Zircon Information Page
Color-Change Diaspore 6.5 - 7 Color Change Diaspore Information Page
Bloodstone 6.5 - 7 Bloodstone Information Page
Hessonite Garnet 6.5 - 7.5 Hessonite Garnet Information Page
Tiger's Eye Matrix 6.5 - 7 Tiger's Eye Information Page
Cat's Eye Diaspore 6.5 - 7 Cat's Eye Diaspore Information Page
Spodumene 6.5 - 7 Spodumene Information Page
Tsavorite Garnet 6.5 - 7.5 Tsavorite Garnet Information Page
Almandine Garnet 6.5 - 7.5 Almandine Garnet Information Page
Peanut Wood 6.5 - 7  
Onyx 6.5 - 7 Onyx Information Page
Carnelian 6.5 - 7 Carnelian Information Page
Pyrope Garnet 6.5 - 7.5 Pyrope Garnet Information Page
Chalcedony 6.5 - 7 Chalcedony Information Page
Rhodolite Garnet 6.5 - 7.5 Rhodolite Garnet Information Page
Sillimanite Cat's Eye 6.5 - 7.5 Sillimanite Information Page
Andesine Labradorite 6 - 6.5 Andesine Labradorite Information Page
Star Moonstone 6 - 6.5 Star Moonstone Information Page
Prehnite 6 - 6.5 Prehnite Information Page
Labradorite 6 - 6.5 Labradorite Information Page
Rainbow Moonstone 6 - 6.5 Rainbow Moonstone Information Page
Rainbow Pyrite 6 - 6.5 Rainbow Pyrite Information Page
Sunstone 6 - 6.5 Sunstone Information Page
Moonstone 6 - 6.5 Moonstone Information Page
Sugilite 6 - 6.5 Sugilite Information Page
Clinohumite 6 Clinohumite Information Page
Maw-Sit-Sit 6 - 7 Maw-sit-sit Information Page
Cassiterite 6 - 7 Cassiterite Information Page
Kyanite 6 - 7 Kyanite Information Page
Star Sunstone 6 - 6.5 Sunstone Information Page
Jadeite 6 - 6.5 Jadeite Information Page
Nephrite Jade 6 - 6.5 Nephrite Jade Information Page
Orthoclase 6 - 6.5 Orthoclase Information Page
Amazonite 6 - 6.5 Amazonite Information Page
Cat's Eye Scapolite 5.5 - 6 Cat's Eye Scapolite Information Page
Moss Opal 5.5 - 6.5 Moss Opal Information Page
Hematite 5.5 - 6.5 Hematite Information Page
Nuummite 5.5 - 6 Nuummite Information Page
Moldavite 5.5 Moldavite Information Page
Opal Doublet 5.5 - 6.5 Opal Information Page
Fire Opal 5.5 - 6.5 Fire Opal Information Page
Rhodonite 5.5 - 6.5 Rhodonite Information Page
Scapolite 5.5 - 6 Scapolite Information Page
Boulder Opal 5.5 - 6.5 Boulder Opal Information Page
Opal 5.5 - 6.5 Opal Information Page
Sodalite 5.5 - 6 Sodalite Information Page
Hackmanite 5.5 - 6 Hackmanite Information Page
Sphene 5 - 5.5 Sphene Information Page
Lapis Lazuli 5 - 6 Lapis Lazuli Information Page
Tremolite-Hexagonite 5 - 6  
Hemimorphite 5 Hemimorphite Information Page
Star Diopside 5 - 6 Chrome Diopside Information Page
Smithsonite 5 Smithsonite Information Page
Cat's Eye Apatite 5 Cat's Eye Apatite Information Page
Turquoise 5 - 6 Turquoise Information Page
Snowflake Obsidian 5 - 5.5 Obsidian Information Page
Apatite 5 Apatite Information Page
Chrome Diopside 5 - 6 Diopside Information Page
Obsidian 5 - 5.5 Obsidian Information Page
Tashmarine Diopside 5 - 6 Tashmarine Diopside Information Page
Larimar 4.5 - 5 Larimar Information Page
Gaspeite 4.5 - 5 Gaspeite Information Page
Charoite 4.5 - 5 Charoite Information Page
Rhodochrosite 4 Rhodoschrosite Information Page
Variscite 4 - 5 Variscite Information Page
Ammolite 4 Ammolite Information Page
Fluorite 4 Fluorite Information Page
Azurite 3.5 - 4 Azurite Information Page
Malachite 3.5 - 4 Malachite Information Page
Sphalerite 3.5 - 4 Sphalerite Information Page
Calcite 3 Calcite Information Page
Coral 3 - 4 Coral Information Page
Verdite 3 Verdite Information Page
Lepidolite 2.5 - 3 Lepidolite Information Page
Pearl 2.5 - 4.5 Pearl Information Page
Chrysocolla 2 - 4 Chrysocolla Information Page
Seraphinite 2 - 4 Seraphinite Information Page
Amber 2 - 2.5 Amber Information Page
  • First Published: September-16-2006
  • Last Updated: November-08-2018
  • © 2005-2019 GemSelect.com all rights reserved.
    Reproduction (text or graphics) without the express written consent of GemSelect.com (SETT Company Ltd.) is strictly prohibited.
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Size and Weight

Gems are always measured in Millimeter (mm)

Dimensions are given as;
length x width x depth,
except for round stones which are;
diameter x depth

Select gems by size, not by weight!
Gem varieties vary in density, so carat weight is not a good indication of size

Note: 1ct = 0.2g

Size Comparison Chart