This guide is designed for those who are new to the world of gemstones and wish to gain a deeper understanding of the terminology and lingo used in the industry. Whether you are a collector, jewelry designer, or simply curious about gemstones, this guide will provide you with the foundation required, to understand the fascinating world of gemstones.

1. Carat: A unit for the measurement of weight – commonly used in the gemstones and jewellery trade. 1 carat is equal to 0.20 grams or 200 milligrams. Use our versatile Carat Converter to convert carats into other units of weight measurement.

2. Clarity Grades: A measure of the number and size of inclusions and blemishes that are present in a gemstone. This clarity is determined using a standard scale used across the industry, and generally from “included” to “flawless”. In general, the following scales are prevalent in the trade:

• Flawless (FL): No inclusions and no blemishes visible under a 10x magnification.
• Internally Flawless (IF): No inclusions visible under a 10x magnification.
• Very, Very Slightly Included (VVS1 & VVS2): Inclusions so slight they are difficult for a skilled grader to see with a 10x magnification.
• Very Slightly Included (VS1 & VS2): Inclusions are observed with effort under a 10x magnification, but can be characterized as minor.
• Slightly Included (SI1 & SI2): Inclusions are noticeable under a 10x magnification.
• Included (I1, I2, & I3): Inclusions are obvious with a 10x magnification, and may affect transparency and brilliance.

3. Facets: Facets are the numerous flat planes on the surface of a gemstone, that are cut and polished in a specific arrangement to enhance its brilliance and scintillation.

4. Gemstone ‘Window’: When a gem is cut too shallow, light passes straight through it, rather than returning to the eye as a sparkle or brilliance. This phenomenon is termed a “window” and is usually present in poorly cut gemstones. You can read more about gemstone windows here.

5. Inclusions: These are internal defects or impurities that are found within the volume of a gemstone. They can take various forms - including bubbles, cracks, minerals, and other substances that penetrate the gemstone as it forms within the surface of the earth. Most natural gemstones available in the market today have some type or form of inclusions, and those that are devoid of them usually cost a fortune.

6. Karat: A Karat, as opposed to a “carat”, refers to the purity of gold in an alloy – the higher the karat number, the purer the gold. A jewel that is 24-karat (stylised as 24k) gold is 100% pure gold, whereas 22k is 91.67% gold, and 18k is 75% gold.

7. Mohs Scale of Mineral Hardness: The Mohs Scale is a relative scale of mineral hardness that was developed by Friedrich Mohs in 1812. It ranges from 1 to 10, where 1 is the softest mineral (talcum) and 10 is the hardest (diamond). The scale is based on the ability of one mineral to scratch another, and minerals are assigned a hardness number based on this ability.

8. Natural vs. Synthetic Gemstones: ‘Natural’ gemstones refer to stones that have been created by nature over millions of years, and are mined from within the surface of the Earth. ‘Synthetic’ or lab-made stones are those that are chemically identical to natural stones, but have been synthesised in laboratories - under controlled conditions and using gemstone seeds. Natural gemstones are usually more valuable because of their rarity.

9. Refractive Index: The refractive index of a gemstone refers to the difference between the speed of light in vacuum and the speed of light within a gemstone. It is a unit-less value, typically ranging from 1.3 to 2.2, that represents how much the light is slowed down as it enters the gemstone. Each gemstone has a unique refractive index - determined by its chemical composition and internal structure. Gemstones with high refractive indices, such as diamond (2.42), tend to have more brilliance (sparkle) and ‘fire’ (scintillation) compared to gemstones with lower refractive indices.

10. Specific Gravity: Ratio between the weight of a stone in air and the weight of an equal volume in water. Each gemstone has a unique specific gravity, which is determined by its chemical composition, crystal structure, and internal organization. Specific gravity can be used to identify and distinguish between different gemstones, as well as to determine the authenticity of a gemstone. For example, the specific gravity of a diamond is approximately 3.52, while the specific gravity of cubic zirconia (a common diamond simulant) is approximately 5.6.

11. Thermal Enhancement: A common treatment process that is applied to gemstones (frequent in yellow and blue sapphires, and rubies) to improve their colour and/or clarity. In most cases, this is a harmless procedure that does not alter the structural integrity of a gemstone, and helps remove certain types of inclusions from within the stone.