Diamond: The Complete Professional Guide
Diamond is the most commercially important gemstone in the world and, for most fine jewellery professionals, the foundation of their business. Yet surprisingly many jewellery professionals have surface-level knowledge of diamond science — the 4Cs at a marketing level, without the deeper physical and gemological understanding that makes for truly compelling, authoritative diamond selling. This article covers the essential diamond science that every professional should command: what diamond is, why it behaves optically the way it does, where it comes from, and how to position it with complete confidence.
Diamond the Mineral
Diamond is pure carbon (C) crystallised in the cubic system under conditions of extreme pressure (approximately 45,000-60,000 atmospheres) and temperature (900-1300 degrees Celsius), at depths of 150 kilometres or more in the Earth’s mantle. Diamond is the hardest natural substance known (Mohs 10), but this exceptional hardness does not mean it is indestructible — diamond has perfect octahedral cleavage in four directions and can be fractured or cleaved by a sharp impact in the right direction.
Diamond’s extraordinary hardness is the result of each carbon atom forming strong covalent bonds with four neighbouring carbon atoms in a tetrahedral arrangement. This three-dimensional network of covalent bonds, extending equally in all directions, creates a structure of maximum strength. The same carbon in graphite (the material in pencil “lead”) forms layered sheets of carbon atoms with weak bonds between layers — making graphite one of the softest minerals despite being the same element as diamond.
Optical Properties: Why Diamond Dazzles
Diamond’s visual performance comes from three optical properties working together: its very high refractive index (2.42), which creates exceptional brilliance through total internal reflection; its high dispersion (0.044), which creates fire (rainbow flashes); and its adamantine lustre, which creates a distinctive surface reflection quality that the eye perceives as unique.
The critical angle for total internal reflection in diamond is only 24.5 degrees — meaning that light hitting any internal surface at more than 24.5 degrees from vertical is completely reflected back into the stone. This is why a well-cut diamond appears full of light from every angle: almost any light that enters is reflected multiple times before exiting through the crown. The round brilliant cut, mathematically optimised by Marcel Tolkowsky in 1919, is designed to maximise this effect while balancing brilliance against fire.
Diamond Origin and Formation
Diamonds form in the Earth’s mantle and are brought to the surface by kimberlite and lamproite volcanic pipes — deep-sourced volcanic eruptions that travel from mantle depths to the surface quickly enough to preserve the diamond without allowing it to revert to graphite. The primary commercial diamond sources include: South Africa (the original kimberlite discovery), Botswana (the world’s largest diamond producer by value), Russia (the Mir, Udachnaya, and Jubilee pipes), Canada (the Ekati, Diavik, and Victor mines), Australia (the Argyle mine, now closed, was the source of rare pink diamonds), and Angola, Zimbabwe, and other African producers.
Diamond Age
Most gem diamonds are between 1 billion and 3.5 billion years old — among the oldest materials accessible to humans. They formed in the mantle during periods of intense geological activity, long before complex life existed on Earth. When you hold a diamond, you are holding something that formed before the oceans took their current configuration, before the dinosaurs, before most of the rock that currently makes up the continents. That age is as extraordinary as any optical property.
Diamond Quality: Beyond the 4Cs
The GIA 4Cs (cut, colour, clarity, carat weight) provide a framework that every professional must know thoroughly. But the most sophisticated diamond selling goes beyond these four metrics to address fluorescence, symmetry, polish, table size, depth percentage, culet condition, and the overall light performance of the specific stone in hand. Two diamonds with identical 4C grades can perform dramatically differently — and only hands-on evaluation with a trained eye identifies which is superior.
Light performance tools (idealscope, ASET scope, hearts-and-arrows viewers) allow objective assessment of how well a diamond returns light. A diamond with a strong AGS Ideal or GIA Excellent cut grade and confirmed hearts-and-arrows symmetry is demonstrably a better-performing stone than one without these indicators, even at the same 4Cs grade level. This is the knowledge that separates diamond professionals from diamond salespeople.
