Natural colored diamonds, often called Fancy Color Diamonds, are prized for their vibrant hues, unlike most diamonds valued for their lack of color. Green is among the rarest colors, joining pink and blue diamonds. This natural rarity makes the green diamond a subject of intense scientific and gemological interest, exploring its unique appearance and the forces that bestow its color.
The Visual Characteristics of Natural Green Diamonds
The appearance of a natural green diamond is not uniform, spanning a range of tones and saturation levels. The color can present as a soft, pale green or a deep, highly saturated forest hue. Most green diamonds are not purely green but possess secondary color modifiers, which gemologists describe as yellowish-green, bluish-green, or grayish-green.
Many natural green diamonds feature color concentrated on the stone’s surface, often called a “green skin.” This outer layer is typical for diamonds exposed to low-penetration natural radiation. When a rough diamond is cut, this superficial color must be carefully preserved. To exhibit a deep, body-wide green color, the diamond must have been exposed to more energetic radiation that penetrates the entire crystal structure.
The Science Behind the Green Hue
The green coloration in a diamond results from the stone’s interaction with natural radiation over millions of years. Unlike most other colored diamonds, which receive color from trace impurities like nitrogen or boron, the green hue comes from structural defects. This exposure occurs when the diamond lies near radioactive minerals, such as uranium or thorium, deep within the Earth.
During this prolonged geological contact, alpha particles, beta particles, or neutrons emitted by the radioactive elements collide with the diamond’s carbon lattice. These energetic particles displace carbon atoms, creating vacancies or “holes” in the crystal structure. These specific defects, known as GR1 centers, alter how the diamond absorbs light. The GR1 centers selectively absorb the red and blue wavelengths of visible light, causing the stone to transmit the green wavelength.
Natural vs. Enhanced Green Diamonds
The process that creates natural green diamonds can be replicated in a laboratory, making the distinction between a natural and an enhanced stone important for value. Treated green diamonds are manufactured by subjecting colorless diamonds to artificial irradiation, often followed by heat treatment. This process creates the same GR1 defects responsible for the natural color, making visual identification challenging.
Gemological laboratories rely on subtle differences to determine the color’s origin. A key indicator of natural origin is the presence of “radiation stains” or color zoning on the unpolished surfaces (“naturals”), which are remnants of the original green skin. Treated stones often exhibit a more uniform color distribution or a pattern related to the facet arrangement. Advanced analytical tools, such as spectroscopy, are necessary to confirm the structural characteristics that separate the natural diamond from its enhanced counterpart. Due to the difficulty in separation, a certification report from a reputable grading institution like the GIA is necessary for any green diamond purchase.
Rarity and Grading
Natural green diamonds are exceptionally rare, accounting for a fraction of a percent of all colored diamonds graded annually. Their formation requires the precise combination of a diamond being in the Earth’s upper layers and proximity to a radioactive source for a sufficient duration. Historically, deposits in South America and Africa have yielded these unique stones.
The value of these diamonds is determined by the Fancy Color Grading Scale, which assesses the intensity of the hue. This scale includes grades such as Faint, Very Light, Light, and the more valuable categories: Fancy Light, Fancy, Fancy Intense, Fancy Vivid, and Fancy Deep. The highest grades, Fancy Vivid and Fancy Deep, represent the most saturated colors and command the highest prices. The presence of a secondary hue, while common, alters the final color description, such as “Fancy Yellowish Green,” affecting the stone’s overall grade and market price.