What's the Mohs Scale of Hardness?

Written By Allie Perry May 24, 2024

The Mohs Scale of hardness and what it means for your jewelry.

When selecting gemstones for your jewelry, there are many important factors to consider. Color, cut, clarity, and carat weight are all crucial details that help you understand a stone’s appearance and cost. However, one of the most important yet often overlooked aspects is the gemstone's hardness. The Mohs scale of hardness is a critical tool that helps you and your jeweler determine the durability and suitability of the gemstones in your jewelry.

What is the Mohs Scale of Hardness?

The Mohs scale of hardness is a qualitative ordinal scale that ranks minerals based on their ability to scratch one another. Developed by German mineralogist Friedrich Mohs in 1812, the scale ranges from 1 (the softest) to 10 (the hardest). Each mineral can scratch those below it on the scale and can be scratched by those above it. Here’s a look at the scale:

10  - Diamond – Scratches all other materials; the hardest natural material.

9 - Corundum (includes sapphire and ruby) – Scratches topaz.

8 - Topaz – Scratches quartz.

7 - Quartz – Scratches feldspar; can scratch glass.

6 - Orthoclase Feldspar – Scratches apatite; can be scratched by steel.

5 - Apatite – Scratches fluorite; can be scratched by a knife.

4 - Fluorite – Scratches calcite; can be scratched by a knife.

3 - Calcite – Scratches gypsum; can be scratched by a copper coin.

2 - Gypsum – Scratches talc; can be scratched by a fingernail.

1 - Talc – Easily scratched by all other materials.

Why is Hardness Important for Jewelry?

The hardness of a gemstone determines its resistance to scratches and abrasion. Choosing a stone with appropriate hardness is incredibly important for jewelry pieces that are worn frequently, such as rings and bracelets, which are more prone to knocks and friction.

The Mohs scale helps you understand a stone’s durability, since harder gemstones are less likely to show wear and tear. For instance, diamonds (Mohs 10) and sapphires (Mohs 9) are popular choices for engagement rings due to their exceptional durability. In contrast, softer stones like opals (Mohs 5.5-6.5) require more careful handling and are better suited for pieces like earrings or pendants that are less exposed to impacts.

Considering the intended use of your jewelry will help you choose the right gemstone. For daily wear items like rings and bracelets, harder stones are preferable. For occasional wear pieces like brooches or special occasion necklaces, stones with lower hardness can be used safely.

Practical Tips for Choosing Gemstones Based on Hardness

1. Consider the Type of Jewelry: For everyday wear items, choose gemstones with a Mohs hardness of 7 or higher. Quartz, topaz, corundum, and diamond are excellent choices.
2. Protect Softer Gemstones: If you love the look of a softer gemstone, consider protective settings that shield the stone from impacts and scratches. Bezel settings, where the metal surrounds the gemstone, offer better protection than prong settings.
3. Regular Inspection and Maintenance: Regardless of the hardness, regularly inspect your jewelry for loose stones or damage. Professional cleaning and maintenance can keep your jewelry looking its best.
4. Educate Yourself on Gemstone Properties: Beyond hardness, factors like cleavage (the tendency to break along certain planes) and toughness (resistance to breaking or chipping) also affect a gemstone’s durability. A gemstone might be hard but not tough (e.g., diamonds have perfect cleavage and can chip if struck).

The more you know…

Understanding the Mohs scale of hardness is essential for making informed decisions when selecting gemstones for jewelry. By considering hardness, you can choose gemstones that will look beautiful and stand the test of time!