Diamonds, in their purest state, are crystalline lattices composed entirely of carbon atoms. A colorless diamond has a perfect atomic structure, allowing light to pass through unimpeded. Color in a diamond signals a disruption to this arrangement, but pink diamonds present a unique scientific mystery. Unlike most colored diamonds, which gain their hue from trace chemical impurities, the pink color arises from a physical anomaly within the stone. This color source is a direct result of immense geological forces that permanently altered the diamond’s internal structure.
Structural Change: The Mechanism of Plastic Deformation
The cause of the pink coloration is plastic deformation. This process involves a permanent change to the diamond’s crystal lattice caused by intense mechanical forces. During this deformation, planes of carbon atoms are physically displaced but are not replaced by foreign elements. Their orderly arrangement is shifted.
This displacement creates internal features called lamellae or slip planes, which are narrow, stressed layers within the diamond structure. These planes are visible under high magnification as lines of stress or graining that run parallel. The presence and density of these parallel planes correlate directly with the diamond’s color intensity. A greater degree of atomic slippage and a higher concentration of these defects result in a deeper, more vivid pink or even red hue.
The Geological Forces Required for Pink Coloration
The intense mechanical forces necessary for plastic deformation are applied after the diamond’s initial formation deep within the Earth’s mantle. Diamonds are forged under extreme heat and pressure approximately 90 to 120 miles beneath the surface. The structural changes occur when the diamond is subjected to colossal shear pressure from tectonic activity.
The movement and collision of Earth’s tectonic plates generate the massive stress required to physically distort the carbon lattice. This pressure bends and twists the diamond structure, forcing atomic layers to slip past each other along certain crystallographic planes. Geological evidence suggests that this deformation often happens during the diamond’s rapid ascent to the surface, typically facilitated by deep-source volcanic eruptions through kimberlite pipes. The unique tectonic history of certain regions, such as the Argyle mine in Australia, provided the conditions for this high-stress event.
How Defects Interact with Light to Produce Pink
The physical defects created by plastic deformation alter how the diamond handles visible light, producing the perceived pink color. White light, containing all colors of the visible spectrum, enters the diamond and encounters these internal slip planes. The structural defects absorb light selectively, centered around 550 nanometers.
This 550 nm wavelength corresponds to the green-yellow region of the visible spectrum. When the green and yellow light components are absorbed by the defects, they are removed from the light beam. The remaining light, transmitted through the stone and reflected back to the observer, is dominated by the complementary colors: red and purple. The combination of these transmitted wavelengths is what the human eye interprets as pink.
Why Pink Diamonds Are Different from Other Colored Diamonds
Pink diamonds are distinct from the two most common types of colored diamonds, yellow and blue, because their color is physical, not chemical. Yellow diamonds derive their coloration from trace amounts of nitrogen atoms incorporated into the carbon lattice. These nitrogen impurities absorb blue light, causing the stone to appear yellow.
Blue diamonds are colored by the presence of boron atoms, which absorb light in the red and yellow regions of the spectrum. In both cases, the color originates from a foreign element integrated into the atomic structure. In contrast, pink diamonds are classified as Type IIa, meaning they are chemically pure and contain little to no nitrogen or boron. Their color is solely a result of the trauma and distortion inflicted upon the pure carbon structure by geological pressure.