What is the Mohs scale?

You’ve probably noticed in our product specifications: when we talk about a stone’s hardness, we’re referring to the Mohs scale. But what exactly is the Mohs scale?

The Mohs scale is a classification system used to measure the hardness of minerals, particularly precious stones and gemstones (the current term for semiprecious stones). It was devised and developed by the German mineralogist Friedrich Mohs in 1812. It ranges from 1 for the softest stones (such as talc) to 10 for the hardest stones (diamond).

How does the hardness scale work?

The hardness of stones is not measured with a precision instrument, but by comparison. Each mineral is tested against ten reference gemstones, which serve as standards:

• Talc
• Gypsum
• Calcite
• Fluorite
• Apatite
• Orthoclase (feldspar)
• Quartz
• Topaz
• Corundum
• Diamond

The principle is simple: if a mineral scratches reference No. 6 but not No. 7, its hardness falls between the two. It is this scratching logic that gives the method its name.

Knowledge of this hardness scale is essential in jewelry making. This tool helps you choose a gemstone based on its intended use. For example, a quartz stone with a hardness of 7 is perfect for creating a ring that will be worn every day. But a calcite stone with a hardness of 3 is better suited for jewelry worn only occasionally.

Find information on the hardness of gemstones in our gemstone glossary or in our guide to gemstones.

Classification of Stones According to the Mohs Scale

Why Hardness Matters in Jewelry Design

Knowing a stone’s hardness allows you to anticipate how it will age in a piece of jewelry. A very hard gemstone will withstand everyday wear and tear, while a softer stone will require more care.

Here are some practical guidelines for your designs:

• Rings and bracelets worn every day: opt for a hardness of 7 or higher (quartz, topaz, corundum). These stones can withstand repeated friction against the skin, clothing, or surfaces.
• Necklaces and earrings: a medium hardness (5 to 6) is generally sufficient, as these pieces are less exposed to impact.
• Decorative pieces or those worn occasionally: a softer stone like calcite (hardness 3) may be suitable, provided it is handled with care.

There are other complementary tools that measure the hardness of materials, particularly natural stones, such asthe Knoop scale,the Brinell scale, andthe Rockwell scale. However, the Mohs scale remains the most widely used method.