Gem Hardness

Mohs' scale of mineral hardness was created by the 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, you have to compare two minerals 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.

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

Mohs original scale is as follows:

Hardness Material Absolute Hardness
1 Talc (Mg3Si4O10(OH)2) 1
2 Gypsum (CaSO42H2O) 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 Diamond 10
Star Ruby 9
Star Sapphire 9
Color-Change Sapphire 9
Ruby 9
Sapphire 9
Chrysoberyl Cat's Eye 8.5
Alexandrite 8.5
Chrysoberyl 8.5
Rutile Topaz 8
Mystic Topaz 8
Imperial Topaz 8
Spinel 8
Topaz 8
Azotic Topaz 8
Beryl 7.5 - 8
Hambergite 7.5
Goshenite 7.5 - 8
Morganite 7.5 - 8
Emerald 7.5 - 8
Cat's Eye Aquamarine 7.5 - 8
Andalusite 7.5
Aquamarine 7.5 - 8
Paraiba Tourmaline 7 - 7.5
Strawberry Quartz 7
Kunzite 7
Quartz Cat's Eye 7
Aventurine 7
Rutile Quartz 7
Chrome Tourmaline 7 - 7.5
Iolite 7 - 7.5
Danburite 7 - 7.5
Smoky Quartz 7
Rubellite Tourmaline 7 - 7.5
Demantoid Garnet 7 - 7.5
Amethyst 7
Cat's Eye Tourmaline 7 - 7.5
Quartz 7
Tourmaline 7 - 7.5
Dumortierite Quartz 7 - 8.5
Star Lemon Quartz 7
Rose Quartz 7
Citrine 7
Ametrine 7
Mystic Quartz 7
Color-Change Garnet 6.5 - 7.5
Agate 6.5 - 7
Color-Change Diaspore 6.5 - 7
Tsavorite Garnet 6.5 - 7.5
Onyx 6.5 - 7
Peanut Wood 6.5 - 7
Tiger's Eye 6.5 - 7
Ruby-Zoisite 6.5 - 7
Sillimanite Cat's Eye 6.5 - 7.5
Hiddenite 6.5 - 7
Zircon 6.5 - 7.5
Bloodstone 6.5 - 7
Hessonite Garnet 6.5 - 7.5
Cat's Eye Diaspore 6.5 - 7
Almandine Garnet 6.5 - 7.5
Carnelian 6.5 - 7
Pyrope Garnet 6.5 - 7.5
Fossil Coral 6.5 - 7
Spodumene 6.5 - 7
Agate Geode 6.5 - 7
Star Garnet 6.5 - 7.5
Chalcedony 6.5 - 7
Rhodolite Garnet 6.5 - 7.5
Mali Garnet 6.5 - 7.5
Axinite 6.5 - 7
Idocrase 6.5
Melanite 6.5 - 7
Tanzanite 6.5 - 7
Peridot 6.5 - 7
Tiger's Eye Matrix 6.5 - 7
Jasper 6.5 - 7
Chrysoprase 6.5 - 7
Dendritic Agate 6.5 - 7
Spessartite Garnet 6.5 - 7.5
Fire Agate 6.5 - 7
Grossularite Garnet 6.5 - 7.5
Star Rose Quartz 6.5 - 7
Clinohumite 6
Prehnite 6 - 6.5
Labradorite 6 - 6.5
Cassiterite 6 - 7
Nephrite Jade 6 - 6.5
Sunstone 6 - 6.5
Moonstone 6 - 6.5
Maw-Sit-Sit 6 - 7
Kyanite 6 - 7
Jadeite 6 - 6.5
Andesine Labradorite 6 - 6.5
Star Moonstone 6 - 6.5
Rainbow Moonstone 6 - 6.5
Rainbow Pyrite 6 - 6.5
Orthoclase 6 - 6.5
Amazonite 6 - 6.5
Sugilite 6 - 6.5
Star Sunstone 6 - 6.5
Moldavite 5.5
Moss Opal 5.5 - 6.5
Sodalite 5.5 - 6
Rhodonite 5.5 - 6.5
Boulder Opal 5.5 - 6.5
Fire Opal 5.5 - 6.5
Hematite 5.5 - 6.5
Cat's Eye Scapolite 5.5 - 6
Hackmanite 5.5 - 6
Nuumite 5.5 - 6
Scapolite 5.5 - 6
Opal 5.5 - 6.5
Opal Doublet 5.5 - 6.5
Smithsonite 5
Snowflake Obsidian 5 - 5.5
Sphene 5 - 5.5
Lapis Lazuli 5 - 6
Tremolite-Hexagonite 5 - 6
Star Diopside 5 - 6
Obsidian 5 - 5.5
Cat's Eye Apatite 5
Tashmarine Diopside 5 - 6
Turquoise 5 - 6
Hemimorphite 5
Apatite 5
Chrome Diopside 5 - 6
Gaspeite 4.5 - 5
Charoite 4.5 - 5
Larimar 4.5 - 5
Fluorite 4
Variscite 4 - 5
Rhodochrosite 4
Ammolite 4
Sphalerite 3.5 - 4
Malachite 3.5 - 4
Azurite 3.5 - 4
Coral 3 - 4
Verdite 3
Calcite 3
Pearl 2.5 - 4.5
Lepidolite 2.5 - 3
Seraphinite 2 - 4
Chrysocolla 2 - 4
Amber 2 - 2.5