Making Gemstone Jewelry: Understanding Mohs’ Hardness Scale for Gemstones

Gemstones and metal jewelry have been beautiful partners for thousands of years. The gemstone cuts have changed through the centuries, as have the jewelry design styles, but now as then, gemstones add beauty, value, and color to metal jewelry designs in a way that nothing else can.

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A 3.46 carat rubellite tourmaline cut by Jim Perkins in the 21st Century Emerald Cut. Photo: Jim Lawson.

There are literally hundreds of different gemstones with more being discovered occasionally, even in modern times. Because they all have different qualities, specifically qualities related to durability like hardness, cleavage, and fracture, not all of them are suitable for use when making gemstone jewelry. Some gems are more suitable for gently worn jewelry, such as earrings and pendants, than for jewelry that can receive hard knocks during daily wear, such as bracelets and rings. It’s important to understand a gemstone’s durability and consider it as you are making gemstone jewelry. Let’s take a closer look at hardness.

To fully understand a gemstone’s hardness–and get an idea of its suitability for jewelry designs–you need to understand the Mohs hardness scale. Learn more about the scale below from jewelry experts Tom and Kay Benham.

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Golden Oval Oro Verde citrine cut by Jim Perkins. Photo by Jim Lawson.

Mohs’ Hardness for Gemstones
By Tom and Kay Benham, Contributing Editors, Lapidary Journal Jewelry Artist

Beginning rockhounds and jewelry makers are often confused by the Mohs hardness scale for rocks and gems. The Mohs hardness scale was set up in the early 1800s by mineralogist Friedrich Mohs, who selected 10 well-known minerals and numbered them in order of scratch hardness, such that a mineral will scratch all minerals having a lower hardness number. It served the purposes of comparison–but because it is a non-linear scale, it does not provide a true indication of the relationship of the various hardnesses.

Mohs' hardness scale for gemstonesAn examination of the chart on the left demonstrates that while corundum (ruby and sapphire) and diamond differ by only one number on the non-linear Mohs Scale, their hardness difference is four times greater on the linear Knoop Scale.

What does this mean to the beginner without any fancy equipment for measuring hardness? Well, by using simple items on hand, rockhounds can easily test for different hardness. Graphite, talc, and gypsum can all be scratched by a fingernail; calcite can be easily scratched with a copper coin; fluorite and apatite can be scratched with a pocket knife; a hardened steel file will scratch orthoclase; and quartz will easily scratch window glass.

You can assemble a simple kit using small samples of all the minerals listed on the Mohs hardness scale for testing the hardness of stones in the field. A diamond is really unnecessary, as it will scratch anything. —Tom and Kay

So how does that affect the gemstones you use when making gemstone jewelry? There are no hard and fast rules, but in general, you should use harder stones for knockabout jewelry types like rings and bracelets, and you can use softer stones for protected pieces like earrings and pendants. Other factors aside, peridot, quartz (including amethyst and citrine), tourmaline, all the jaspers and agates, most garnets, and topaz are some common stones generally considered hard enough for setting in rings and bracelets, with hardnesses ranging from 6-1/2 to 8.

Softer stones like amber, coral, fluorite, and apatite (hardnesses ranging from 2 to 5) would be safer worn in earrings and pendants, in general, or at least with substantial protective settings when set in rings and bracelets. As I said above, though, there are no hard rules. We’ve all seen my favorite gemstone, pearl (Mohs’ hardness of 3-4), featured in rings and bracelets and not always with protective settings. Jewelry like this should be worn with care–but most folks don’t wear pearls on the soccer field anyway!

If you’d like to learn more about gemstones, making gemstone jewelry, and find inspiring ways to cut and/or set gemstones in your own jewelry designs, check out some of my favorite gem-related resources below–and use coupon code TREAT10 today and tomorrow only to save $10 off your $30 purchase!

Lapidary Journal Jewelry Artist magazine
Metalsmith Essentials: Setting Stones with Bezels with Lexi Erickson DVD
Gemstone Settings: The Jewelry Maker’s Guide to Styles and Techniques book
Metalsmith Essentials: Special Stone Settings: Saddle and Strap with Michael Boyd DVD
Colored Stone 2009-2010 magazine CD collection (including the special pearl issue!)
10 Gemstone Pendants project eBook

Happy Halloween!

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