Hardness of Gemstones (Mohs Scale)

What is the hardness of gemstones?

The hardness of a gemstone refers to how resistant it is to scratches. This is measured using the Mohs scale , a scale from 1 to 10, with 1 being the softest and 10 the hardest. The scale was developed by Friedrich Mohs in 1812 and is used worldwide in mineralogy.

• 1 (soft) : Talc, a mineral that can be easily scratched with a fingernail.
• 10 (hard) : Diamond, the hardest natural material in the world.

Why is hardness important?

The hardness of a gemstone determines its durability and whether it's suitable for everyday use, such as in jewelry. Softer stones, such as opal (5-6) or turquoise (5-6), are more susceptible to damage and require more care. Harder stones, such as sapphire (9) and diamond (10), are more resistant to wear and tear and are often chosen for wedding rings and other jewelry worn daily.

How is hardness measured?

The Mohs scale compares gemstones to reference materials: one stone can scratch another stone of a lower value, but not the other way around. For example, a quartz (7) can scratch glass (about 5.5), but is not itself scratched by glass.

Tips for caring for gemstones

• Soft stones : Avoid contact with hard surfaces and store them separately from harder stones.
• Harder stones : Although less sensitive, they can still be damaged by extreme pressure.
• Clean gemstones gently with water and a soft cloth, unless otherwise advised.

Here is a chart showing the Mohs scale of hardness for various gemstones:

Mohs scale	Mineral/Gemstone	Particulars
1	Talk	Softest mineral, can be scratched with a fingernail.
2	Plaster	Easy to scratch with a fingernail.
3	Calcite	Can be scratched with a copper coin.
4	Fluorite	Relatively soft, can be scratched with a knife.
5	Apatite	Moderate hardness, used in tooth enamel.
6	Orthoclase (feldspar)	Can scratch glass, but not extremely durable.
7	Quartz	Common gemstones such as amethyst, citrine, and rose quartz.
8	Topaz	Hard, often used in jewelry.
9	Corundum (sapphire, ruby)	Very hard, only diamond is harder.
10	Diamond	Hardest natural material, scratch resistant unless contacted with another diamond.

Explanation

• Intermediate values: There can also be stones with intermediate values, such as turquoise (5-6), opal (5.5-6.5) and peridot (6.5-7).
• Durability: Hardness is just one aspect of durability; cleavage and fracture behavior also play a role. For example, diamond is hard, but can cleave under strong impact.

Identifying the hardness of gemstones is essential for understanding their durability and how to care for them. Here are some ways to identify or test a gemstone's hardness: