Tips for stone care

What is the strongest stone on the planet?

It is possible to visually distinguish stones from each other by color, but what to do if the shades are almost the same? There are so many cases in mineralogy when one stone was mistaken for another, and as a result a new, previously unknown mineral was discovered. At first glance, it is very difficult to distinguish leucosapphire from colorless topaz, or ruby ​​from garnet. To do this, gemologists conduct many tests, among which there is a very important one – testing the stone for hardness. In this article we will talk in more detail about the hardness scale and its creator. In the photo: German scientist and mineralogist, creator of the hardness scale – Friedrich Moos. German geologist Friedrich Mohs moved to Austria in 1801 to work for a mining company. He was also hired by a wealthy Austrian banker to store and identify his extensive mineral collection. Mohs’ tasks included sorting collection minerals and identifying stones unknown to science. Friedrich Moos knew that gems were classified according to their chemical composition, but wanted to simplify, improve and speed up this process. In 1812, he created a hardness scale that was initially criticized by the mineralogical community, but eventually achieved worldwide fame. Friedrich Mohs followed the botanists’ lead and grouped minerals according to their physical characteristics, starting with how hard they were. According to some reports, Moos took plaster and was unable to scratch any other stone with it. He conditionally defined its hardness as 1. The scientist arranged the following minerals in order of increasing hardness. The last tenth stone turned out to be a diamond, since no other nugget could scratch it. However, Moos is not the first to do this. For the first time, in 77 BC, Pliny the Elder compared the hardness of diamond and quartz. He described his research in the book Naturalis Historia, and Friedrich Moos decided to continue the ordinal ranking system of Pliny the Elder. So he came up with a set of 10 hardness values ​​that could be determined relative to each other by scratching. In the photo: Mohs hardness scale. The hardness of a mineral usually refers to the resistance that its surface exhibits when you try to scratch it with another stone or object.

  • minerals with hardness 1 and 2, such as talc and gypsum, are considered soft and can be easily damaged even with a fingernail;
  • stones with a hardness of 3 to 6, such as calcite, fluorite, apatite and orthoclase, are considered medium hard. They can be damaged with a pocketknife or a coin;
  • gems over 6 points are called hard.

Crystals generally provide a consistent hardness, but some stones have unique characteristics and may have different hardnesses. For example, minerals such as garnet or quartz can have several different chemical compositions, so their hardness will vary from 6,5 to 7,5.

The Mohs hardness scale has been used in mineralogy and geology for over 200 years. Thanks to this table, many specialists in the field determine which group of minerals the found nugget belongs to.

In the photo: “Starlight” pendant from the Maxim Demidov jewelry house.

Jewelry metals can also be rated on the Mohs hardness scale:

  • Gold – from 2,5 to 3 points. Gold is a very soft metal and it is for this reason that it is never found in pure form in jewelry. To make the products suitable for daily wear, it is necessary to add an alloy in the form of silver, copper, zinc, palladium or other metals. Such alloys give gold the desired hardness.
  • Platinum – from 4 to 4,5 points. The silvery-white metal is almost twice as hard as gold. The material is so durable that jewelry can be made from pure metal, without adding a ligature.

In the photo: platinum ring “Elsker” and gold ring “Heart Ties” from the Maxim Demidov jewelry house.

Diamond has a 10 on the hardness scale and is considered the hardest substance. Jewelers know all the intricacies of processing this precious stone and take into account important parameters when cutting. For example, an unprocessed crystal has edges that are practically impossible to cut. And there are also those that, if the master moves incorrectly, can split the gem. Understanding such subtleties saves time and allows you to create the best diamond with minimal waste.

In the photo: Monopoly diamond ring from the Maxim Demidov jewelry house.

The best quality rubies and sapphires are used to create jewelry. These crystals are rated 9 on the Mohs scale, which means they are second only to diamond in hardness. Thanks to these almost ideal parameters, the stones are perfect for industrial purposes. Non-jewelry corundums are used in the production of laser systems and transistors, in medicine and dentistry, in the production of watch movements, etc.

In the photo: a ring with a Milonga ruby ​​and a ring with a sapphire “Royal Attribute” from the Maxim Demidov jewelry house.

Topaz and spinel score 8 on the Mohs scale. And the hardness of the beryl group: aquamarine, morganite, emerald, in some cases can vary from 7,5 to 8 points. These are also quite hard gems that can not only sparkle in jewelry, but also be useful in production: aircraft and astronautics, high-precision instruments, musical instruments, ceramics and dyes that have increased resistance to overheating. But even in this case, only non-jewelry quality samples are used in production.

In the photo: ring with topaz “Fantasy of Youth” and ring with spinel “Delight of Sunset” from the Maxim Demidov jewelry house.

The most fragile and delicate stone in the Maxim Demidov jewelry treasury is pearls. It has a hardness ranging from 2,5 to 4 on the Mohs scale. Mother of pearl beads can be easily scratched by any sharp object. But at the same time, pearls are considered a fairly strong stone and are almost impossible to split.

In the photo: pearl set “Longi” from the Maxim Demidov jewelry house.

Although the Mohs scale is an indicator of mineral hardness, it does not take into account an important feature – the structure of gemstones. Any gem needs careful treatment and care. Even a diamond that has a score of 10 can break if accidentally dropped, since the stone is fragile. Always exercise caution when wearing any gemstone jewelry to ensure that these timeless pieces do not lose their beauty.

The Mohs table is only a means of determining whether stones belong to a certain type. But it is not a table of distribution of stones by cost. Some people believe that if a diamond scores 10 on the Mohs scale, it is the most expensive of all gems. However, it is not. The price of precious stones is influenced by the quantity of their reserves in the world, as well as quality characteristics: clarity, color, weight and cut.

You can see more details about what parameters make up the cost in our video “How much do precious stones cost?”

The Maxim Demidov jewelry house invites you to enjoy the shine of precious gems.

Diamond is a mineral that is outstanding in every way. Like an unsightly doll (a nugget diamond really does not look like anything special in appearance), after cutting it turns into a delightful butterfly – a diamond worth hundreds, thousands and even millions of dollars.

But it’s not only the unearthly radiance and fantastic price that makes this stone stand out among its peers. Diamond is the hardest of all minerals, which determines the widest scope of its application. Not every diamond can turn into a diamond – only the purest and largest stones deserve this honor.

But even a small and cloudy nugget will not be thrown away as unnecessary, but will find application in the watch or nuclear industry, quantum computers or microelectronics, and, at worst, in the production of abrasive, drilling and cutting equipment. It’s Diamond!

General information about diamonds

Do you know the formula of diamond? Even a preschooler who has no idea about chemistry can remember it. It’s just C, which means diamonds are pure carbon (ideally, of course).

What had to happen for carbon to turn into diamond? Many hypotheses have been put forward on this matter. The most convincing of them claims that diamonds are formed at very great depths (over 200 km) and under tremendous pressure – there carbon forms a special cubic lattice inherent in diamonds. During volcanic processes, carbon crystals are carried closer to the surface, where they are discovered by diamond miners.

This process is very slow: the age of diamonds is measured in hundreds of millions, or even billions of years. So when, during intensive mining, diamond-bearing kimberlite pipes and other rocks are depleted, the reserves of this stone will dry up for a very long time.

According to scientific data, some diamonds are of extraterrestrial origin. They came to us with meteorites or came to us as a result of a supernova explosion. It is assumed that some of them are much older than the solar system!

There are a lot of diamonds on Earth, but only a tiny part of them can be turned into diamonds. The purest and largest diamonds (the so-called “Cape”) are mined in Africa, and Russian reserves of this mineral are concentrated mainly in Yakutia.

Among the most outstanding properties of diamond are the following:

  • unsurpassed hardness – 10 on the Mohs scale;
  • the highest thermal conductivity among solids – 900–2300 W/(m K);
  • vanishingly low coefficient of friction on metal (in air);
  • refractoriness and resistance to high temperatures;
  • resistance to most aggressive acids and alkalis;
  • high refractive index of rays combined with transparency;
  • the ability to luminesce (glow) in x-rays and ultraviolet light.

Diamonds are not only white, but also colored. Brown and yellow colors reduce the cost of a diamond, blue, blue, pink, red, green – increase it to sky-high heights.

The main characteristic that decides the fate of a rough diamond is transparency (“clear water”). That is why black diamonds (carbonados) have long been considered exclusively technical. However, occasionally you come across evenly colored black diamonds that retain some transparency and characteristic shine. They are mind-bogglingly expensive.

How is the hardness of a diamond measured?

Even a child knows that the strength of a diamond is incredible (meaning its hardness, not its resistance to shock). It is taken as the basic value on all measurement scales. And this is surprising, because diamond’s closest relatives, graphite and coal, which have the same elementary chemical composition, cannot boast of outstanding strength.

The secret of diamond hardness lies in the unique conditions of its formation: high temperatures and incredible pressure. With them, carbon atoms form a unique cubic crystal lattice. This determines the incredible hardness of the final substance, which can exist in natural conditions for billions of years!

Unsurpassed hardness allows diamond to be used in the production of equipment for drilling and ultra-precise cutting. No substance can resist the standard!

Mohs scale

The first successful attempt to create a scale of hardness of materials belongs to the German mineralogist Friedrich Mohs. Despite the fact that this system was presented to the scientific community back in 1811, it continues to be used to this day, mainly in application to minerals of natural origin (including precious stones).

The hardness of a diamond on the Mohs scale is 10, that is, this mineral was taken as an absolute: a priori there is nothing harder than it. The basis of this test is scratching. If a scratch remains on the surface of the test sample, then it is a priori softer than the standard.

The second place in hardness on the classical Mohs scale is held by corundum, which includes sapphires and rubies – 9 points. You can only scratch them with a diamond!

However, the very rare natural moissanite and its artificial analog carborundum (chemical formula SiC) have a strength of as much as 9,5 Mohs points. By the way, carborundum often replaces diamond both in industry and in the production of jewelry. Visually, it is practically indistinguishable from its noble brother, but costs an order of magnitude cheaper!

Everyone knows that diamond has greater strength than graphite, despite the identical chemical composition. However, not everyone knows that they are at diametrically opposite ends of the Mohs scale. The hardness of graphite is comparable to that of talc, and this is only one!

Rockwell system

With the advent of synthetic materials and super-hard alloys, the generally accepted Mohs scale has become inconvenient. Many systems were proposed, but in the metallurgical industry the Rockwell scale (more precisely, the Rockwells, because there were two of them, distant relatives with the same surname) took root most of all.

The Rockwell hardness of diamond is not measured – it is taken as a standard and the main working tool. The Rockwell measuring machine visually resembles a sewing machine, but instead of a needle, a diamond cone is used, and fabric replaces the material being tested.

The sample is exposed to a diamond cone with a given pressure for several seconds, then the parameters of the dent are assessed on a letter-numeric scale.

What’s harder than diamond?

Many attempts have been made to create or find in nature a material stronger than diamond. So far they have not been successful: obsidan, titanium, super-hard alloys, all kinds of innovative materials cannot compete with the noble standard. Moreover: many chemists and physicists even argue that substances stronger than diamond (more precisely, harder) cannot exist.

The most famous and scandalous story involves a substance called lonsdaleite, which in a chemical and physical sense is a hexagonal diamond. In the 60s of the last century, this mineral was synthesized artificially, and a little later it was discovered in small quantities in meteorite craters.

In 2009, a group of Chinese scientists published a sensational paper claiming that lonsdaleite is more than half as hard as cubic diamond (as we know it). Unfortunately, these data turned out to be a hoax and were not confirmed even by the calculations in the above work.

The most successful attempt to create a substance harder than diamond was made quite recently, in 2021. A duo of American scientists managed to produce hexagonal diamonds from graphite using targeted explosions. The resulting samples demonstrated better sound conductivity than classic cubic diamond, which theoretically indicates greater hardness.

Unfortunately, it has not yet been possible to test the theoretical calculations of American scientists experimentally. And the disgraced lonsdaleite, obtained from graphite by exposure to colossal pressure, shows a strength of only 7-8 points on the Mohs scale. And it’s unlikely to be used: it consists of crystals visible only under a microscope, and obtaining this substance is fantastically expensive.

There are other substances that are not much inferior to diamond in hardness: fullerites, all kinds of boron compounds, carbyne, and so on. They are slightly softer than diamond, but often surpass it in other characteristics: strength, resistance to chemical attack and ultra-high temperatures.

A stronger substance can be created from cubic diamond (for example, using nanoengineering). The Japanese succeeded, but how to process this unprecedentedly hard material?

Can a diamond be scratched or broken with a hammer?

Based on the above, we can conclude: it is impossible to scratch a diamond. This makes it possible to quickly identify rough glass counterfeits that are easily scratched by a steel needle or nail file. True, imitation diamonds like cubic zirconia, and even more so carborundum, cannot be recognized in this way.

But there are plenty of substances stronger than diamond – and even steel! This means breaking a diamond is quite possible. Naturally, the stone will calmly survive a fall from a considerable height, and even if you step on it, nothing critical will happen. But if you hit the diamond with force with a hammer, it will crack, otherwise it will crumble into small crumbs.

But you shouldn’t do this: the experiment will be too expensive, and the world will lose another diamond that has been formed over hundreds of millions of years!

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