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Hardness vs. Durability

By Yagé Enigmus

When considering which gemstone to purchase or wear in jewellery, it is important to choose a stone that will be appropriate for the desired use and able to withstand the stresses that it may endure. The choice of stone for an engagement ring may be very different from the stones used in other custom made jewellery, as it will be worn on the hard where it is more exposed and will likely be worn every day.

Many people are familiar with certain stones having a certain ‘hardness’, the most famous example of which is diamond, possessing a hardness rating of 10 on the Mohs hardness scale and being known as one of the hardest naturally occurring substances. But what is hardness, and how does it relate to a stone’s durability?

Durability is something’s general resistance to damage, with hardness only being one element of durability. Hardness refers to a substance’s ability to withstand localized force without deformation, and this can encompass scratching, indentation, and other types of deformation.

When discussing gemstones hardness is primarily a measure of scratch resistance. The Mohs hardness scale is a relative scale from 1 to 10 measuring different materials’ ability to reduce one another via scratching or abrasion. The most popular gemstones frequently rank quite high on the Mohs scale; ruby and sapphire rank at 9, while emerald ranks at 7.5, making sapphire jewellery and emerald jewellery among some of the more durable options. This is the scale most often used for initially assessing the durability of a gemstone and determining how to care for it, but many other factors play into a stone’s durability, some of which have a direct influence on hardness.

The toughness of a material is another major component of its durability, which can be thought of as a substance’s ability to absorb force and resist breaking under stress. In the case of more crystalline materials, toughness separately addresses resistance to general breakage and resistance fractures. The primary variables behind toughness are strength and ductility.

Strength refers to the overall ability to withstand force without any structural deformation, and ductility is a measure of how much deformation a material can take before breaking.

Both hardness and toughness play into the impact resistance of a stone, but ultimately all aspects of a gemstone’s durability are determined by the chemical composition of the gem and the geometric characteristics of its internal structure. Diamond for example ranks at 10 on the Mohs scale, but if hit with enough force at the right angle can be cleaved perfectly along all three axes due to the internal crystal structure, and this was actually how diamonds were cut in the ancient world before further development in gem cutting techniques. Topaz ranks at 8 on the Mohs scale but also possesses a structure that can be perfectly cleaved along one of its axes.

Conversely tourmaline, a softer gem ranking at 7-7.5 on the Mohs scale, has a highly complex chemical composition and internal structure, lending it a significant degree of overall impact resistance even though it has lower scratch resistance.

One must consider the overall quality of the stone in question when judging its durability as inclusions and impurities in a stone can affect many of the variables discussed above. Additionally the cut and shape of a gemstone may have an effect on how force is delivered to the material and how it responds to stress.

Durability Table
(Co-Created with David Saad)

The following table is an approximation of gemstone durability based on both empirical data, as well as over fifty years of experience manufacturing coloured gemstone jewellery. Please understand that very good or excellent durability does not mean that a gem is ‘indestructible’ by any means, we have seen thousands of chipped and abraded diamonds, sapphires and rubies.

ALL gemstones and jewellery should be treated as fragile.

Durability

Material

Comments

Poor

Talc, Gypsum (Selenite), Mica (Lepidolite, Muscovite, Biotite), Cerussite, Chlorite (Seraphinite), Calcite

Talc, gypsum and mica can be damaged with human fingernails 


Mica has perfect basal cleavage, and calcite has three planes of perfect cleavage, making these already soft and easily scratched minerals highly susceptible to damage upon impact 


These gemstones are not durable enough for most jewellery.

Fair

Opal, Pearl, Ammolite, Coral, Sphene, Fluorite, Sphalerite, Apatite, Larimar, Rhodochrosite, Scolecite, Kyanite

These materials are durable enough for wear, but have low impact and scratch resistance, so care must be taken in order to avoid damage. 


Kyanite has different hardness along different axes, drastically affecting impact resistance 


Any of these gems will make wonderful necklace/pendant/earring gems, but are not suitable to wear 24/7 (while you sleep), and if worn daily/near daily in a ring, may need to be repolished every 7-10 years.

Moderate

Orthoclase Feldspar (Classic Moonstone), Plagioclase Feldspar (Labradorite, Rainbow Moonstone, Sunstone) Microcline Feldspar (Amazonite), Rhodonite, Grandidierite, Zoisite (Tanzanite, Thulite), Lapis Lazuli, Malachite, Turquoise

These materials are durable enough for most custom jewellery if care is taken when being worn 


All feldspars have two planes of good cleavage, making them less impact resistant 


Most of these gems have been worn in jewellery for millennia and examples of jewellery with these gems are seen in museums around the world, often still in excellent condition, if worn 24/7 (while you sleep) these may need to be repolished every 10-15 years. 


These can be worn daily with minimal damage and passed on as heirloom jewellery.

Good

Emerald, Quartz (Amethyst, Citrine, Prasiolite, Ametrine), Peridot, Grossular Garnet (Hessonite, Tsavorite), Andradite Garnet (Demantoid, Topazolite), Zircon, Spodumene (Kunzite, Hiddenite), Iolite, Chalcedony (Carnelian, Agate, Chrysoprase), Prehnite, Amber

These materials are highly durable and can be worn in a wide variety of environments, some care must be taken when designing and creating jewellery with these gems to make it possible to wear 24/7 (while sleeping) 


These gems can be made into heirloom/legacy/generational jewellery and other than Amber which is extremely easily repolished, are unlikely to need to be repolished in your lifetime unless worn 24/7

Very Good

Aquamarine, Morganite, Heliodor, Goshenite, Tourmaline (Elbaite,

Dravite, Liddicoatite, Schorl),

Jadeite, Nephrite, Pyrope Garnet, Almandine Garnet, Rhodolite Garnet, Spessartite Garnet, Uvarovite Garnet, Chrysoberyl (Alexandrite, Cymophane), Spinel, Topaz

These materials are extremely durable and can be worn in almost any jewellery design throughout one’s lifetime 


Topaz is the least impact resistant due to perfect basal cleavage


Thousands of examples of millennia-old jewellery can be found with these gems and are excellent stones for heirloom jewellery. Some care must be taken when designing and creating jewellery with these gems to make it possible to wear 24/7 (while sleeping).

Excellent

Sapphire, Ruby, Diamond

These materials are exceedingly durable and can be worn in any bespoke jewellery throughout one’s lifetime.


Diamond is the least impact resistant due to three planes of perfect cleavage


Although all gems should be treated as fragile, these are by far the most durable and can be worn 24/7 (while sleeping) for an entire lifetime with minimal/no changes to the design of the jewellery to protect them and no need to repolish in your lifetime regardless of the application

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