Choosing your stone: Stone hardness, durability, and long term wearability

Not all stones have been created with equally desirable qualities. The earth has worked hard on making beautiful creations that may or may not serve you well as an engagement ring stone with daily wear. This blog post should help you feel informed about your stone decision. 

Hardness

When gemologists speak about the hardness of a stone, what they mean is the level of resistance to being scratched. For instance, glass is not 'hard' in the gemstone world. And, diamonds are so hard that diamonds can cut other diamonds. Diamonds can scratch all other stones and glass. 

Durability is something to keep in mind if you would like a stone that will require little care over its lifetime. If your stone scratches because you chose a softer stone, it will require repolishing to bring it back to it's original look, and only until it scratches again.

Removing a gemstone to re-polish it is a process that removes stone, shrinking it's carat weight and size. The difficulty of having to replace prongs or prong tips with speacilty laser welding tools can and will add to the cost of your piece's care.

Stability

The stability of the stones is different than the resistance to scratching (a.k.a. hardness.) Stability is resistance to heat, acid, and other chemicals that can cause damage. 

Toughness

Any stone, including a diamond, will be damaged and break if it is hit hard enough in the right place. Toughness is a measure of how well a gem can survive an impact and resist breaking, chipping, or cracking.

 

Which stones are the most durable for every day wear?

It is generally recommended that stones for engagement/wedding rings should be no softer than a level 8 on the Mohs scale. This allows for high amounts of wearability, meaning lower risk of being scratched.

Diamond

Hardest Gemstone

Mohs: 10/10

Absolute Hardness: 10,060 kp/mm

Stability: High 

Toughness: Medium

Wearability: 10/10

If you google the hardness scale of a diamond and other gems, what you'll usually see is a Mohs hardness scale. The Mohs scale is very misleading because it's numbers allow you to think that sapphires and rubies are close to the hardness of a diamond, but they are not. The Moh's scale shows you in 10 steps which stones can scratch other stones. What you should be more aware of is the absolute hardness of your stone.

The only similar stone in hardness to a diamond is a natural or lab grown Moissanite.

Alexandrite, Sapphire & Ruby

Mohs scale: 9/10 

Absolute hardness: 2000 kp/mm (vs. diamond: 10,060)

Stability: High

Toughness: Medium

Wearability: 9/10

As you can see in the above numbers as compared to diamonds, the second batch of gemstones that are recommended for daily wearing are Corundum or Chrysoberyl. Corundum in white, greens, and blues is called a Sapphire, and the same stone in reds and pinks is called a Ruby. Chrysoberyl called Alexandrite can change from a range of reds/oranges/purples to deep greens/blues, and is very rare.

Emerald, Topaz, Spinel, Morganite, Aquamarine

Mohs: ~8/10 

Absolute hardness: 1500-2000 kp/mm (vs. diamond: 10,060)

Stability: Medium

Toughness:  Medium

Wearability: 6-8/10

Heat (fire) exposure is not recommended and since jewelry is made with melting metals with fire, this can cause issues with long term care like repairs, prong retips, and more.

Care must be taken with chemicals. Clean with mild soap.

These gemstones are still considered to have high stability and wearability for a day to day basis. However, you may consider removing this gemstone when doing hard labor, lifting/moving objects (like during moving day), and working with tools. Please care for your stone with mild soap, avoiding highly acidic jewelery cleaning chemicals.

 

Further reading...

Understanding Gemstone Durability

Gemstone wearability by the GIA

 

 

July 10, 2018 by Midwinter Co