February 15, 2021

Get to know fine and precious stones

What gives stones value and how do you choose one?

First, what defines fine and precious stones? They are attractive quality gems often used in jewelry. They are sought after mainly for their appearance, but they must meet other criteria in order to be mounted on jewelry such as rings or earrings. For the various uses, it is therefore necessary to take into account their hardness and their stability.

Officially, there are four stones that are said to be precious:

The diamond
The emerald
The ruby
The sapphire

The other stones are said to be fine. The list of stones deserving the characterization of "fine" is determined by the CIBJO . These gems are of mineral origin and are solids composed of an ordered atomic structure with a specific chemical composition for each type of stone. It is a crystallized material with a variety of crystalline organization dividing them into several species of stones. The traces of different chemical elements in the crystalline structure will create a range of colors specific to each appellation.

There are also stones of organic and non-mineral origin which are:

Amber
Coral
Jet
Mother-of-pearl
Pearls

The science that studies these stones is gemology.

Stone quality factors

Rarity and demand are, as in many areas, the reasons that greatly influence the value of a stone, but it is the following criteria that determine its quality.

The colour

The color of a stone makes it more or less attractive to whoever looks at it. This is a personal preference, but generally the richer, saturated and rarer the pigment the higher the value of the stone. Also if a stone is rare because it exists in small numbers on earth, but it is not in high demand, it will be undervalued.

The cut

Cutting is the way of cutting a rough crystal to make it react strategically with light and reflect it to create the maximum brilliance. When he cuts a stone, the lapidary creates by means of polishing a set of facets which act like a panoply of small mirrors to redirect the light which enters the stone and gives it a shiny appearance. This physical phenomenon is called refraction. Each stone has a different refractive capacity and therefore has a higher or lower index, for example the diamond has a refractive index of 2.42.

The cut of a stone is very important to give a higher value to the raw crystal, if the cut of the stone is of lower quality, it will not shine as much and will be much less attractive. However, to have a nice cut you often have to sacrifice a good part of the rough. So the lapidary must make a compromise between having a larger stone and a medium size or a smaller stone, but with a very nice cut.

The carat of the stones

The carat (abbreviation ct) is a unit of mass measurement for stones. It is different from the karat of metals which represents their level of purity. There are 5 carats in 1 gram and there are 100 points in a carat. So a stone of 0.5ct is equal to a stone of 50pt (points).

Stones are generally sold by weight and the greater the total mass of the stone, the greater the value per carat. For example, the same type of stone can cost $1000 per carat for a stone of 0.5ct or $7000 per carat for a stone exceeding 1.0ct. It is for this reason that the cut of the stone is sometimes sacrificed in favor of the carat, as some people prefer the coarseness to the brilliance.

Clarity

A stone can have any desired level of opacity. Some stones are naturally opaque such as turquoise or lapis lazuli. Others are translucent like opals and moonstone. For transparent stones like sapphires and tanzanites, impurities are mostly undesirable. These impurities are called inclusions. Clarity is the amount of inclusions visible to the naked eye, magnifying glass or microscope. Maximum clarity is sought and increases the value. To have a better quality-price ratio, we can accept inclusions invisible to the naked eye, since this is the way that your stone will most often be admired.

Hardness

Hardness is the ability of a material to resist being scratched by a material with a different hardness. For gems and minerals, the Mohs scale is used to assess and classify this resistance. This scale assigns a score from 1 to 10 to minerals by comparing which mineral is able to scratch it.

In the field of jewelry, a stone must have a certain hardness to be mounted on a piece of jewelry and keep its original appearance even with daily use. For a ring, which is the type of jewelry with the greatest potential for damaging the stones, we recommend a hardness of at least 6.5. As we use our hands constantly, the risk of abrasion is great and a stone that is too soft will quickly scratch and lose its luster. Indeed, from 6 it is considered more appropriate to mount stones with this hardness as a necklace, brooch or earrings.

The hardest stone is diamond with a rating of 10, it can only be scratched by diamond. Other examples:

Hardness	Mineral
7	Quartz
8	Topaz
9	Corundum (sapphire and ruby)
10	Diamond

The hardness does not take into account the resistance to shocks which can split even the diamond.

The source

Fine and precious stones are formed by physical and chemical processes occurring naturally all over our planet. A specific stone is created in limited quantities in specific places in the world, called a deposit. For example, demantoid garnet is found in the Ural Mountains of Russia and Namibia. Stones from the Russian deposit are rarer than those found in Namibia and are therefore generally more valuable. So it is interesting and important to know the origin of your stone to understand its value.

Treatments

It is possible to change the color of some stones with heat or radiation treatments. They can be heated in the laboratory to high temperatures (about 500+/-100 degrees Celsius) to modify or intensify their color. They can also be lightly irradiated to increase their richness in color or change their tone. These treatments make it possible to transform natural stones and make them more attractive to the eyes. According to certain schools of thought, these practices devalue the stones.

The real value of the stones

A variety of technical criteria are used to classify and qualify fine and precious stones. These characteristics and information are important in choosing a stone that will suit your jewelry and your lifestyle. However, ultimately the most important question to ask is: are you in love with this stone?