Gemology is the science that studies gems, i.e. precious and semi-precious stones such as diamonds, emeralds, sapphires and rubies. This discipline requires in-depth knowledge of geology, physics, chemistry and crystallography.
Gemologists therefore use specialized techniques to assess the quality and value of gems, such as observing with a magnifying glass, measuring hardness, density, color, transparency and fluorescence. They can also identify synthetic or treated stones, as well as their imitations.
What is a gem?
A gem is a precious or fine stone with ornamental value. It is also used to refer to minerals (quartz, turquoise, jade, etc.) and animal or vegetable substances such as pearls, coral or amber. Stones that can be called “gems” must therefore be natural, and have a certain degree of resistance to be easily handled without scratching or deteriorating. These stones must have a beautiful color.
In 2002, French legislation abolished the designations “precious stones”, “ornamental stones” and “semi-precious stones”. To harmonize with the nomenclature of the CIBJO (Commission Internationale de Bijouterie, de Joaillerie et d’Orfèvrerie), the term “ gemstone ” was adopted. It includes precious stones, ornamental stones and semi-precious stones.
Differences between gemstones and precious stones
The main difference between gemstones and semi-precious stones is their rarity and economic value. Stones such as diamonds, sapphires, rubies and emeralds are considered precious because of their rarity, beauty and high value. On the other hand, semi-precious stones such as amethyst, garnet, citrine and aquamarine are more common and less expensive.
These stones are now grouped together under the name “gemstones”. However, each gem has specific characteristics that distinguish it from the others.
What is a gemstone?
A gemstone is a rare, beautiful and durable stone used in jewelry. The four best-known gemstones are :
- Diamond
- emerald
- Sapphire
- Ruby
Gems are natural products extracted from crystals found in deep-seated rocks or sedimentary deposits. They are called precious because of their specific qualities.
Diamonds
Diamonds are precious stones from different parts of the world (Russia, Botswana, Congo, Australia…). Very rare, it is used in jewelry (rings, bracelets, necklaces, etc.). It’s worth noting that this transparent mineral attracts by its beauty and purity. Diamond is a precious stone composed of pure carbon crystallized under specific temperature and pressure conditions.
Diamond’s uniqueness lies essentially in its extreme hardness, known since the dawn of time. For it is the hardest natural mineral found in nature. The stone comes in a variety of colors: pink, green, blue, white, black, yellow and more. But only diamonds can scratch diamonds.
Ruby
Ruby is classified in the corundum family of minerals. It is the red variety of this mineral species. This stone therefore has an intense, deep color. Its name comes from the Latin ruber, meaning “red”. The distinctive feature of this gemstone is, of course, its sublime red color. Ruby owes its coloring to the presence of chromium atoms in its composition.
In addition to its magnificent red hue, it symbolizes passion, love and loyalty. Ruby, whose main countries of origin are Mozambique and Burma, is used to make jewelry such as rings (and wedding bands), crowns and more.
Sapphire
Like ruby, sapphire comes from corundum, i.e. aluminum oxide. This stone can take on different colors, but not red (green, pink, white or orange). Blue sapphire is the best-known, and has been used to make precious objects such as the engagement ring of the UK royal family. The world’s main sapphire producers are Burma, Sri Lanka, Australia and Madagascar.
Emerald
Emerald is a mineral belonging to the silicate family. A member of the beryl family, it is distinguished by its green hue, which comes from traces of chromium, iron and vanadium. In jewelry, this precious stone is used to make necklaces, pearls, rings and all kinds of jewelry and brooches. Colombia, Zambia and Brazil are the main emerald producers.
What is a gemstone?
A fine stone is a gem that is not considered precious, but is nevertheless used in jewelry. They are often more common and less expensive than so-called precious stones. The CIBJO considers them to be “minerals extracted from natural deposits”. They include a wide variety of stones, such as :
- Agate
- Amethyst
- Citrine
- Rock crystal
- Epidote
- Garnet
- Onyx
- Tiger’s eye
- Peridot
- Smoky quartz
- Pink quartz
- Hematoid quartz
- Spinel
- Tourmaline
- Topaz
- Tanzanite
- Aquamarine
- Zircon
In 1970, CIBJO drew up a complete list of gemstones. The difference between gemstones and precious stones is not in their price. Some fine gems are indeed more expensive and rarer than precious stones. Other criteria such as quality, clarity, color and weight are used to define their value.
What is a carat?
This is the name given to two units of measurement used in jewelry. In each field, it implies different interpretations that are sometimes mistakenly confused.
The origin of the word
The word carat comes from the Greek “Keration”, meaning “carob seed” or “small weight”. The name was inspired by the fruit of the carob tree, which grows naturally around the Mediterranean. These contain tiny seeds of exceptional regularity.
In ancient times, carob seeds were used as a unit of measurement. Merchants used them in the gold trade. One carob seed was considered toweigh 200 mg (0.2 g), and this mass remained unchanged.
What is a carat for a metal?
The carat (noted ct or k) is a measure of the purity of precious metals such as gold or silver. It is equivalent to 1⁄24 of the total mass of an alloy. A 24-carat ingot is therefore equivalent to 100% pure gold. The carat thus makes it possible to determine the level of pure gold contained in a piece of jewelry. If a piece of jewelry has 18 carats, this means it contains 75% fine gold.
What is a carat for a stone?
In jewelry, it’s a unit of measurement for the mass of gems. In 1907, the Fourth General Conference on Weights and Measures established the equivalent of the carat in grams. It was decided that one carat (ct, k or kt) corresponds to 200 mg, or 0.2 g. A rare stone measuring five carats therefore weighs one gram.
How do I choose the right gemstone?
Given the vast collection of gemstones on offer, choosing the right one can be difficult. Here are some important criteria to bear in mind when buying gemstones.
Hardness
This is one of the key points to consider when choosing a quality stone. One of its essential characteristics is its ability to resist scratches and withstand intense use. The Mohs scale is used to evaluate hardness. The maximum is 10 and the minimum is 1. So the closer a gem is to ten, the harder it will be.
Color
Color is the other decisive criterion for choosing an authentic rare or fine stone. The rule is: don’t choose a mineral that’s too dark or too light. There’s a simple test you can do to check. Expose the stone to daylight or artificial light. A stone that’s too light will let a lot of light through, unlike a mineral that’s too dark, which will not be very permeable because it’s too thick.
Purity
Stones are classified by level according to the defects they present. Level 1 gems are flawless. They are totally pure. Level 2 gems have inclusions. Level 3 gems may have a crack, a well-marked inclusion or other defects. The purer the stone, the higher its value.
Gem size
Gems come in a variety of faceted sizes. Choose a cut that suits the stone’s intended use, whether as jewelry or a decorative object. And if you opt for faceted stones, inspect them from several angles. Check the quality of polishing, the regularity and symmetry of the facets. With these criteria in mind, you’ll be well on your way to choosing the right stone jewelry.
