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The Durability of Gemstones

Understanding gemstone durability and hardness is essential for anyone interested in jewellery, antique or otherwise – especially if you’re looking for the perfect alternative gemstone engagement ring.

Not only does durability play into how suitable for daily wear a piece of jewellery is, understanding the factors that constitute a gemstone’s durability helps determine how to look after them and prevent damage. This article considers the three determinants of a gemstone’s durability – hardness, toughness, and stability.

Gemstone hardness

A gemstone’s hardness is a good indicator of how well it will resist scratches and abrasions. The Mohs scale ranks gems on a relative scale based on their scratch hardness. Therefore, while corundum (ruby or sapphire) is a 9, a diamond at 10 is many times harder – only a diamond can scratch a diamond. Corundum can scratch itself, topaz (8), quartz (7), and anything softer. Topaz can scratch itself, quartz (7), and anything lower on the scale, etc.

The Mohs Hardness Scale

Developed by German mineralogist Fredrich Mohs in 1812, the Mohs Hardness Scale consists of ten readily available minerals of particular hardness. The scale is used to compare a mineral’s scratch resistance and hardness and ranges from soft minerals (e.g., talc) to the hardest on earth, diamond.

Mineral Hardness
Talc 1
Gypsum 2
Calcite 3
Fluorite 4
Apatite 5
Feldspar 6
Quartz 7
Topaz 8
Corundum 9
Diamond 10

Selected gemstones ordered by Mohs Hardness

Gemstone Hardness
Pyrophyllite 1
Amber 2
Wulfenite 3
Ammonite 4
Lapis Lazuli 5
Amazonite 6
Amethyst, citrine 7
Topaz 8
Sapphire, ruby 9
Diamond 10

Gemstone toughness

Bear in mind the Mohs Hardness Scale is non-linear and therefore doesn’t provide a true reflection of each gemstone’s hardness. It’s also important to remember that, although a gem may feature high on the Mohs Hardness Scale, it doesn’t mean that the stone won’t break – this is where toughness comes in.

Fracture toughness

The toughness and breakage resistance of a gemstone is determined by its internal structure, or more specifically, its atomic composition and bond strength. Toughness is rated from poor, fair, good, excellent, to exceptional. For instance, crystal formed gemstones are weaker due to the stone’s internal inclusions. And despite diamond being the hardest natural substance on earth, it is rated as ‘good’ for toughness because if it’s hit at a certain angle, it can fracture and break.

Corundum (e.g., ruby and sapphire) are the most durable gemstones when combining hardness and toughness – 8 on Mohs Scale/’Excellent’ toughness. Therefore, if you’re considering an engagement ring for everyday wear, sapphireruby, and diamond are smart, durable choices.

Gemstone stability

External elements including light, heat, and chemicals can cause a stone to change colour or break.

Light

For example, both amethyst and citrine are light-sensitive and dull if exposed to light for prolonged periods, underscoring the importance of suitable storage.

Temperature

Temperature is another crucial factor, as sudden changes can prompt thermal shock, causing cracks, fractures, and potential breakages.

Humidity

Some gemstones are susceptible to the humidity of their surroundings. Opals, for example, often lose moisture in low humidity or when exposed to heat, causing them to crack. Vaults and safes usually have extremely low humidity levels and will dry out opals. On the other hand, prolonged exposure to water can damage some gems, such as amber, azurite, and malachite.

Chemicals

We come into contact with chemicals daily, so it’s crucial to consider them when wearing gemstone jewellery. Cleaning, swimming, showering, and perfume are just some activities and everyday essentials containing abrasive chemicals that can damage gemstone jewellery.

How to clean gemstone jewellery

Generally, a small dish of soapy water is all you need – be mindful of ultrasonic cleaners, as the tiny vibrations may cause a stone to break or lose its colouring if heat treated.  Therefore, be sure to always check whether the jewellery you wish to clean is suitable and follow a thorough, step-by-step jewellery cleaning guide.