The Mohs Scale of Hardness Explained

It’s general knowledge that some gemstones are harder than others, but what exactly does that mean and are there any implications? There are certain stones, such as a diamond, that are considered durable for everyday wear, but there are others that would likely get damaged, such as tanzanite. Instead of listing these out individually or relying on research in every situation where you would need to know such a thing, we have the Mohs scale of hardness. The Mohs scale of hardness is a tool that is used to measure how hard a mineral is, based on their ability to scratch each other.

Origins of the Mohs Scale

The Mohs Scale of Hardness was created by Friedrich Mohs in 1812. Mohs was a German mineralogist who had a strong interest in geology and studied at the Mining Academy in Freiberg, Germany. During his studies, he learned about minerals including their relative hardness, which was previously described simply using words such as hard or soft. Unfortunately this was not a very precise unit of measurement, especially because there are many levels between hard and soft. Noticing this problem, Mohs created the Mohs Scale of Hardness, which was a simple way to determine how hard a mineral is.

When formulating his scale, Mohs selected ten minerals that ranged in hardness and he arranged them from hardest to softest, giving them a value of 10 to 1 according to which ones could scratch each other. This created a standardized scale that is still used today. Mohs scale was quickly adopted within the scientific community, since it was seen as simple and practical. Even now it is taught in all types of courses such as gemology, geology, and mineralogy.

As with most things, there have been changes over time–although Mohs basic scale has remained the same. With technological advancements, there is no need to use other minerals to scratch each other in order to determine where they fall on the scale. There are now other testing methods and instruments that can be used. You can also use common items such as a fingernail, copper coin, knife blade, or a steel file, which all have assigned levels of hardness, to discern where a mineral would fall on the Mohs scale.

What is the Mohs Scale for Gems?

Let’s take a look at each level on the Mohs scale and the corresponding gemstones. This is important because softer stones are not ideal for jewelry, as they can get easily damaged. It’s best to choose a gemstone that is on the higher end of the scale to avoid replacing it often, or not feeling comfortable wearing the jewelry.

Hardness 10:
Mineral: Diamond
Popular Gemstones: colorless diamonds, fancy colored diamonds

Hardness 9:
Mineral: Corundum
Popular Gemstones: ruby, sapphire

Hardness 8:
Mineral: Topaz, Spinel
Popular Gemstones: blue topaz, imperial topaz, mystic topaz, red spinel, blue spinel, pink spinel

Hardness 7.5 - 8:
Mineral: Beryl
Popular Gemstones: emerald, aquamarine, morganite

Hardness 7.5:
Mineral: Zircon
Popular Gemstone: Blue zircon

Hardness 7 - 7.5:
Mineral: Tourmaline
Popular Gemstones: paraiba tourmaline, rubellite, watermelon tourmaline, green tourmaline

Hardness 7:
Mineral: Quartz
Popular Gemstones: amethyst, citrine, rose quartz

Hardness 6.5 - 7.5:
Mineral: Garnet
Popular Gemstones: tsavorite, spessartite

Hardness 6.5 - 7:
Mineral: Olivine, Zoisite
Popular Gemstones: peridot, tanzanite

Hardness 6 - 7:
Mineral: Jadeite
Popular Gemstones: jade

Hardness 5.5 - 6.5:
Mineral: Opal
Popular Gemstones: precious opal, fire opal

Hardness 5 - 6:
Mineral: Turquoise
Popular Gemstones: Turquoise

Once you reach 5 on the scale, there aren’t typically any popular gemstones that can be mentioned, as they are far too soft to be safely used in jewelry.

Hardness 5:
Mineral: Apatite (found in various colors and sometimes cut as a gemstone for collectors, but not used in jewelry due to how brittle it is)

Hardness 4:
Mineral: Fluorite (Found in a variety of colors, fluorite is sometimes used in ornamental carvings, but is not suitable for jewelry because it can scratch and break easily.)

Hardness 3:
Mineral: Calcite (Used in industrial applications such as cement production, calcite is too soft for use in jewelry.)

Hardness 2:
Mineral: Gypsum (Selenite, which is a form of gypsum, is sometimes used in carvings, but since it can be scratched with a fingernail, it is nowhere near durable enough for use in jewelry.)

Hardness 1:
Mineral: Talc (Extremely soft and can be scratched with a fingernail, it feels greasy to the touch and is used often as a lubricant. It goes without saying that it cannot be used in jewelry.)

These softer minerals are not suitable for jewelry for several reasons. Since jewelry is so often worn and can be knocked against things, these minerals will easily scratch. They also have good cleavage, meaning they can split easily, especially if they were put into jewelry. Softer minerals are also very difficult for jewelers to work with because even with the most careful touch, they can be damaged.

Things to Consider with Softer Gemstones

When working with gemstones that are suitable for jewelry, but still a little softer (5-7 on Mohs scale), there are some things to keep in mind. You may want to consider setting these stones in a type of jewelry that would be less likely to come into contact with a hard surface to sustain damage. Some suggestions are earrings, pendants, and pins. There are also some setting styles that offer more protection for your gemstone by surrounding it with more metal, therefore protecting it in the case of potential damage. We would recommend either a full or partial bezel, where the stone is either partially or completely surrounded with metal. Also, setting these stones with a lower profile will reduce the chances of coming into contact with a hard surface.

It’s also recommended to remove jewelry during any activity that may cause damage, for example cleaning, gardening, working out, swimming, showering, etc. Keep your jewelry stored in a closed container where it won’t be exposed to chemicals or dust, and make sure that each piece of jewelry is separate and not touching each other, as this is how stone scratching damage often occurs. To be safe, have your jewelry inspected every six months if worn regularly, and repair any damage promptly.

Final Considerations

The Mohs Scale of Hardness is a necessary tool for both jewelers and consumers alike to understand the durability of specific gemstones and whether they would be appropriate for use in jewelry or not. Harder stones, such as diamonds and rubies, are ideal for everyday wear, but softer stones such as calcite and apatite are too easily damaged for jewelry use. There are stones that fall in the 5 - 7 range on Mohs scale that can still be used successfully for jewelry, but require particular care. With careful consideration, it’s definitely possible to maintain the integrity of beautiful jewelry, even with slightly softer stones, by using strategic setting styles.

If you’re ever trying to determine if a particular stone is appropriate for your desired use, be sure to reference Mohs Scale of Hardness.