GemSelect Newsletter: The Strength of Gemstones - Hardness and Durability
When most people think of gemstones and strength, hardness is usually the first thing that comes to mind. The universal scale used to measure hardness and scratch-resistance was devised by Friedrich Mohs. The beauty behind Mohs scale of mineral hardness is its simplicity. The scale is fairly easy to understand, whether you're a jeweler or an ever-learning lover of collecting gemstones, especially since it utilizes a basic numerical system that ranges from 1 to 10; the higher the number score, the harder the material.
On Mohs scale, diamond tops the scale at 10, making it the world's hardest natural substance (there is no 10.5), while talc scores the lowest with a hardness of 1. In between diamond and talc is apatite, a relatively lesser-known gem. The fact that it's the mineral that defines 5 on the most well-known scale of hardness, it's surprising that few people are even aware of apatite. Mohs scale isn't a linear scale, which means it doesn't specify how much harder or softer a specific material is when compared to another material with a different hardness. For example, both sapphire and ruby have a hardness of 9, and even though diamond is only one point higher in hardness, it's nearly 4 times harder than the corundum gemstones.
The use of Mohs scale isn't limited to only the gem and jewelry trade. In fact, you'll often see Mohs ratings being used when shopping for smartphones and tablets. Since everyone knows that steel is pretty tough, smartphone and tablet manufacturers often describe their screens to be harder than steel, which is pretty clever marketing since it's true. But then again, who hasn't had a "tough-as-nails" screen shatter on them, even if there wasn't a scratch on the screen before the inevitable happened? This is an example of when hardness is often confused with strength.
Although diamond is the hardest, it isn't the toughest. This is because of other attributes, such as cleavage and tenacity. In the gem trade, when referring to cleavage, it has nothing to do with a low-cut ladies shirt. It refers to the ability or inability of a mineral to be split or cleaved by a knock or blow. Some gem types, including diamond, tanzanite, and topaz, exhibit perfect cleavage, which means they can easily split if accidentally dropped or knocked - not so tough anymore, huh?
There are many gemstones that exhibit good, indistinct or no cleavage at all. These include sapphire, aquamarine, ruby, and spinel, for example. These gems aren't nearly as hard as diamond, but you'll be surprised just how tough and durable they are. With relatively good hardness and lack of perfect cleavage, there are many gem types that are perfectly ideal for daily-wearing jewelry, once again proving that it's not just about being hard.
Another factor to consider when it comes to overall toughness, and one that's often overlooked, is a gemstone's crystal structure. A good example of crystal formation's impact on durability is that of diamond and graphite, which are both made of carbon. However, carbon with diamond's crystal habit is the hardest material on Earth. On the other hand, carbon graphite rates less than 1 on Mohs scale. Even so, graphite is often used for the making of high-strength industrial components, including parts for automobiles, aircraft, and sports equipment. For being such a softy, graphite can handle the wear and tear of commercial airplanes, making it considerably tough!
Other gemstones that may not be hard, but have a very tough structure, include jadeite and nephrite. You likely won't find a bangle made entirely from diamond or topaz, especially since a single blow would cause it to shatter like glass. However, jadeite and nephrite have such toughness, they're quite often carved into pure jade jewelry designs, including bangles, rings, and other ornamental carvings.
In addition to cleavage, hardness, and crystal structure, some gemstones are simply sensitive to external elements, such as chemicals, the environment, or pressure. Examples of gemstones that can be sensitive and require a little extra care, include peridot (gem-quality olivine), which is sensitive to pressure, and pink kunzite, which is physically durable, but it's color is known to fade with prolonged exposure to strong light.
When sensitivity is combined with softness, the strength or durability of stones will be much lower. For example, opals are sensitive to humidity and lack hardness (5.5 to 6.5 on the Mohs scale). Pearl is another gem type that's both sensitive and relatively soft. Even though pearl and opal lack both the durability of jadeite and the hardness of diamond, it certainly doesn't stop people from wearing them in jewelry. In fact, opals and pearls are some of the most popular jewelry gemstones in the world!
There are also some treatments that can render gemstones weaker or stronger. Although many gemstone treatments are frowned upon, when beautiful gemstones lack durability, many treatments are actually welcomed. This is the case with opal, ammolite, and also turquoise. With ammolite, it wouldn't be possible to wear it without stabilization or impregnation, and on top of that, most are offered as doublets or triplets. Turquoise is another popular gemstone that benefits from a toughening treatment. Turquoise in its purest form is too fragile to wear as jewelry, which means it's almost always stabilized when used for jewelry.
It's important to keep in mind that the hardness of a gem refers only to its resistance to scratching, whereas overall strength, durability, and toughness, take into consideration all of the above. It is the combination of these factors that determine the wearability of a gemstone, especially when it comes to jewelry designs that are worn every day. If you're looking for a gemstone that can endure daily wear and tear, don't focus too much on its hardness like many consumers do.
Some of the most popular and most wearable gemstones, include jade, sapphire, ruby, spinel, tourmaline, and many varieties of quartz and garnet. Having said that, even if a certain gemstone that's caught your eye has low durability, it doesn't mean you can't wear it. Every gemstone can be worn one way or another, it will just simply require a bit more care, that's all!
Scissor-Cut Aquamarine: Although we covered aquamarine in last month's newsletter, we couldn't help but feature it again in this month too. Why? Because it's not everyday that we come across such stunningly well-cut and brilliantly-colored specimens. Our recent addition of aquamarines this month included some of the best material we've seen in years. Many of them are large, exceptionally clean, and feature beautiful scissor-cut facets that maximize their blue sparkles.
Cat's Eye Apatite: Very rarely do we see apatite with excellent color and clarity, and almost never, will we see one with such a stunningly sharp cat's eye effect, too! As mentioned above, apatite is a lesser-known gem, so it's not a gemstone for people that prefer popular jewelry trends. This cat's eye apatite is better suited for one that can appreciate rarity combined with high-quality. It is also an excellent option for fans of cat's eyes in general. The well-centered eye is distinctively straight and clear, making it an especially unique and a true collector piece!
Fantasy Cut & Fancy Carved Blue Topaz: Gemstone cutting has traditionally been thought of more as a craft rather than as an art. Fancy gemstone cutting started as an art years ago in Europe and America, which many attribute to Bernd Munsteiner, a German gem cutter from Idar-Oberstein. Recently, we come across a number of gemstones that are far from ordinary, bordering the line of fantasy and art. Although we're just starting to build on our collection, take a look at some of our stunning examples of cutting at its finest.
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Happy Gem Hunting!
Your friends at GemSelect
- First Published: February-20-2018
- Last Updated: April-12-2018
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