The Language of Diamond Structure

A diamond is not just a shiny stone—it is a complex geometric structure engineered to interact with light in specific ways. Understanding the basic anatomy of a diamond helps you appreciate why cut quality matters so much, why proportions matter, and how light behaves inside the stone.

The Basic Parts of a Diamond

The Crown

The crown is the upper portion of the diamond, extending from the girdle (the outer edge) up to the table (the flat top). The crown contains the facets that receive incoming light and refract it into the stone. The angle and quality of the crown facets determine how much light enters the diamond and how it is distributed.

A well-cut crown captures light efficiently and reflects it back through the crown in a balanced pattern of brilliance and fire. A poorly cut crown allows light to escape through the sides or bottom of the diamond.

The Table

The table is the large, flat facet on the top of the diamond. It is the largest single facet on most diamond shapes and is the primary window through which light enters and exits the stone. The table percentage (the width of the table relative to the total width of the diamond) is one of the most important proportions.

A table that is too large allows light to pass straight through without reflecting internally, making the diamond appear washed out. A table that is too small restricts light entry, reducing brilliance. The ideal table percentage for round brilliants is approximately 53-58%.

The Girdle

The girdle is the outer edge of the diamond, the narrow band that separates the crown from the pavilion. It is the widest part of the diamond and the reference point for measuring diameter. The girdle can be faceted, polished, or bruted (rough-cut). It is also where diamonds are typically inscribed with their certificate numbers, visible only under magnification.

The Pavilion

The pavilion is the lower portion of the diamond, extending from the girdle down to the culet (the bottom point). The pavilion facets reflect light internally, creating the internal light return that produces a diamond is brilliance. The pavilion depth (the height from girdle to culet) is one of the most critical proportions.

A pavilion that is too deep traps light and makes the diamond appear dark in the center. A pavilion that is too shallow allows light to escape through the sides, making the diamond appear dull. The ideal pavilion depth for round brilliants is approximately 43%.

The Culet

The culet is the small facet at the bottom point of the diamond, parallel to the table. In some diamonds, the culet is a pointed culet (no facet, just a sharp point). In older cuts, a larger culet facet was common; in modern cuts, the culet is typically very small or pointed to maximize light return.

A culet that is too large can create a visible dark spot in the center of the diamond when viewed from the top, called a fish-eye effect.

Facet Patterns

The number and arrangement of facets define the character of each diamond shape. A round brilliant has 58 facets (or 57 if the culet is pointed). Step cuts like emerald and asscher have facets arranged in parallel rows that step inward like the edges of a staircase, producing a hall-of-mirrors reflection pattern rather than intense sparkle.

How Light Behaves Inside a Diamond

A well-cut diamond is designed to maximize total internal reflection. When light enters the diamond through the crown, it travels through the stone and reflects off the pavilion facets back toward the crown, where it exits as visible brilliance. If the pavilion angle is too steep, light reflects too many times before exiting, reducing intensity. If too shallow, light exits without sufficient internal reflection, reducing brilliance.

Proportions and Light Performance

The key proportions that determine light performance are table percentage, total depth percentage, crown angle, pavilion depth, star length, and lower girdle half length. These numbers are all interconnected—a change in one affects the others. This is why a certificate is valuable: it documents the specific proportions of the individual diamond.

At Aranc

We provide proportion data on all our diamonds and can explain how the specific proportions of any diamond affect its light performance.