Gemmology is the study of gems. It includes the analysis of their physical, chemical, and optical characteristics. If you're new to the fascinating world of gemstones, it can be helpful to understand some commonly used technical terms. Here's a handy glossary to help you navigate the language of gemology:
Carats :
A carat is a unit of weight used to measure gemstones. One carat is equal to 0.2 grams.
Chatoyancy :
A light effect similar to the pupil of a cat's eye, observed in some cabochon-cut stones such as cat's eye chrysoberyl. Inclusions in the stone, such as channels, are responsible for this effect.
Clarity :
The clarity of a gemstone refers to the presence or absence of inclusions and flaws visible to the naked eye or a loupe.
Cleavage :
It is the ability of a gemstone to split along specific planes of its crystal structure under the effect of shock or pressure. This is called a cleavage plane , which is the direction in which a gemstone can fracture or break most easily. This is an important characteristic to consider when cutting and polishing stones.
Color :
Color is one of the most important characteristics of a gemstone. Gemologists evaluate color in terms of hue, saturation, and tone.
Crown :
The crown of a gemstone refers to the upper part of the stone, including the table (the flat surface at the top) and the surrounding facets.
Cylinder head :
The pavilion of a gemstone refers to the lower (often pointed) part of the stone, located below the crown.
The line between the crown and the cylinder head is called the laminated . For the diamond we speak of roundist but it's exactly the same thing.
Dispersion :
The ability of a stone to decompose white light into its different colors, as a prism can. The resulting decomposition is called "fire."
Dubbing :
An optical phenomenon that occurs when a transparent material (in our case, a stone) has high birefringence. When light passes through the stone, it is split into two rays. These two rays follow separate paths through the stone, resulting in a duplication or "doubling" of the images seen through the stone. This phenomenon is particularly visible at the edges of the stone. It is commonly observed in certain gemstones such as sphene, zircon, and peridot.
Hardness and Toughness :
The hardness of a gemstone refers to its resistance to scratches and scuffs. It is measured on the Mohs hardness scale, which ranges from 1 (very soft) to 10 (very hard). For example, diamond, the hardest mineral, has a hardness of 10, while talc, the softest mineral, has a hardness of 1.
It is important to note that hardness does not take into account impact strength, called toughness . For example, diamond is very hard but has low toughness, while jadeite jade has high impact resistance despite its average hardness on the Mohs scale.
Gemstones commonly used in jewelry have a hardness range of 6 to 10 on the Mohs scale, ensuring adequate resistance to scratches and damage.
Glow :
The luster of a gemstone refers to the shine of its surface when exposed to light.
Facet :
A flat, polished surface cut from a gemstone to enhance its brilliance and beauty.
Gem :
A precious stone, natural or synthetic, that can be used in jewelry making for its beauty, rarity, and durability. This also includes certain organic materials of animal or plant origin such as pearls, coral, amber, etc.
Inclusions :
Inclusions are imperfections within a gemstone, such as cracks, foreign crystals, trapped liquid...
Among crystalline inclusions, we distinguish between positive and negative crystals. Positive crystals are a foreign crystal that was present at the time of crystal formation. Negative crystals are vacancies (emptiness) that take the form of the host crystal. It is sometimes difficult to differentiate positive crystals from negative crystals because the shape of the negative crystal takes the form of a crystal.
Description :
In the context of gemology, a libel is the name given to an air/gas bubble trapped in a void within a gemstone, which contains liquid. It is called a shrinkage bubble because it forms when the liquid trapped within the stone cools. They are generally only visible under a magnifying glass or microscope.
Magnifying glass :
A loupe is a tool used by gemologists to closely examine the characteristics of gemstones. Loupes with 10x magnification are typically used.
Summary :
This is a man-made stone. It has exactly the same chemical composition, and the same physical and optical properties as its natural counterpart. However, it does not have the same history... natural stones are generally a few million to several billion years old, for the oldest.
Treatments :
Treatments are processes applied to gemstones to improve their appearance or durability, such as heating, diffusion, or filling.
By understanding these basic terms, you'll be better equipped to choose and appreciate the beautiful gemstones that will enrich your collection. If you have any additional questions, please don't hesitate to contact us.
