Diamonds are famous for their brilliance and for being the hardest natural material known. They are symbols of love, luxury and endurance, but their story begins deep inside the Earth, under extreme conditions, over very long periods of time. Today, diamonds are also produced in laboratories, which has changed the market. This guide explains how diamonds form, what determines their value and what to know before buying one.
Advertisement
What is a diamond?
A diamond is made of carbon atoms arranged in a very strong, three-dimensional crystal structure. Each carbon atom is bonded to four others, creating an extremely rigid network. This structure makes diamond the hardest natural material known, with a rating of 10 on the Mohs hardness scale. Graphite, used in pencils, is also pure carbon, but its atoms are arranged in layers, which makes it soft. The difference shows how structure can change the properties of a material.
How natural diamonds form
Most natural diamonds formed about 150 to 200 kilometers (roughly 90 to 120 miles) below the Earth's surface, in the mantle, under very high pressure and temperatures above 1,000°C. Many are between 1 and 3.5 billion years old, much older than most life on Earth.
They were carried toward the surface by deep, fast volcanic eruptions, inside rocks called kimberlites and lamproites. These eruptions created vertical structures known as kimberlite pipes, which are the main sources of mined diamonds. Diamonds can also be found in riverbeds and coastal deposits, after erosion carried them away from their original rocks.
The 4Cs
The Gemological Institute of America (GIA) created a widely used system to describe diamond quality:
Advertisement
Cut
Cut refers to how well the diamond is shaped and polished: its proportions, symmetry and finish. A well-cut diamond reflects light efficiently, creating brilliance and sparkle. Cut is different from shape, such as round, oval, princess or emerald.
Color
Most gem diamonds are graded on a scale from colorless to light yellow or brown. Colorless diamonds are usually more valuable. Diamonds with strong, attractive colors, such as blue, pink or vivid yellow, are called "fancy color" diamonds and are graded differently.
Clarity
Clarity describes the presence of tiny internal features, called inclusions, and external marks, called blemishes. Most are invisible to the naked eye. Fewer and smaller inclusions usually mean higher value.
Carat
Carat is the unit of weight for gems. One carat equals 0.2 grams. Larger diamonds are rarer, so price per carat usually increases with size.
Natural and lab-grown diamonds
Lab-grown diamonds are created in laboratories using two main methods:
- HPHT (high pressure, high temperature): reproduces conditions similar to those in the Earth's mantle.
- CVD (chemical vapor deposition): carbon from a gas is deposited layer by layer onto a diamond seed.
Lab-grown diamonds have the same chemical and physical properties as natural diamonds, and specialized equipment is needed to tell them apart. They are usually much less expensive. When buying, ask whether the diamond is natural or lab-grown and request a grading report from a recognized laboratory, which should disclose its origin.
Simulants, such as cubic zirconia and moissanite, are different materials that look similar but are not diamonds.
Famous diamonds
- Cullinan: found in South Africa in 1905, it weighed about 3,106 carats in its rough form, the largest gem-quality diamond ever found. It was cut into several stones, some of which are part of the British Crown Jewels.
- Hope Diamond: a deep blue diamond on display at the Smithsonian's National Museum of Natural History in Washington, D.C., surrounded by legends.
- Koh-i-Noor: a historic diamond with a long and disputed history, also part of the British Crown Jewels.
Where diamonds are mined
Major producers include Russia, Botswana, Canada, the Democratic Republic of the Congo and South Africa. Brazil was one of the world's main diamond sources in the 18th century, especially in Minas Gerais, where the town of Diamantina was named after the stones.
Ethics and sourcing
In some conflicts, diamonds were used to finance armed groups, giving rise to the term "conflict diamonds" or "blood diamonds." The Kimberley Process, launched in 2003, is an international certification system intended to prevent the trade of these stones. Critics argue that it has limitations, so many buyers also look for retailers that explain their sourcing policies.
Uses beyond jewelry
Because of their hardness and thermal conductivity, diamonds are used in cutting tools, drills, saws, abrasives and polishing. Scientists also study diamond for electronics, high-pressure experiments and quantum technologies. Most industrial diamonds are synthetic.
Tips for buying a diamond
- Set a budget before shopping.
- Compare the 4Cs, not just the size.
- Prioritize cut for brilliance.
- Ask for a grading report from a recognized laboratory.
- Ask whether the stone is natural or lab-grown.
- Buy from reputable sellers with clear return policies.
- Consider insurance for valuable pieces.
Diamond shapes
The shape is the outline of the diamond seen from above. The round brilliant is the most popular, designed to maximize sparkle. Other common shapes include oval, princess (square), cushion, emerald (rectangular with step facets), pear, marquise and heart. Each shape reflects light differently, and some can make a diamond appear larger for its weight.
Caring for diamond jewelry
Diamonds are hard but can chip if struck at certain angles. Clean them with warm water, mild soap and a soft brush, store them separately to avoid scratching other jewelry, and have settings checked periodically by a jeweler.
Frequently asked questions
Are diamonds the hardest material?
They are the hardest natural material known, rating 10 on the Mohs scale.
Are lab-grown diamonds real diamonds?
Yes. They have the same chemical and physical properties as natural diamonds.
What does carat mean?
It is a unit of weight. One carat equals 0.2 grams.
What is the largest diamond ever found?
The Cullinan, found in South Africa in 1905, with about 3,106 carats in its rough state, is the largest gem-quality diamond ever found.
What is the Kimberley Process?
An international certification system created to prevent the trade of conflict diamonds.
How old are natural diamonds?
Many are between 1 and 3.5 billion years old.
Conclusion
Diamonds are the result of extreme natural forces acting over billions of years, or of advanced laboratory technology. Understanding how they form, how they are graded and the difference between natural and lab-grown stones helps you appreciate their beauty and make informed, responsible choices.