The Cause of Colors

Here lightly brushed in and with variegated play, there firmly laid on or, as it were, solidified—the colors of gemstones manifest themselves in crystalline clarity and total beauty. The investigation and explanation of gem colors forms one of the most exciting chapters of gemmology. Optics and chemistry mesh in with the highly topical science of atomic structure and forces.

In technical language a distinction is made between self- or inherently-colored (idiochromatic) minerals and foreign or extraneously-colored (allochromatic) minerals. In the idiochromatic ones the pigmenting element is a constituent part of the chemical structure and thus an inherent (integral) component. Such gemstones as almandine, peridot, spessartite, malachite, rhodochrosite, rhodonite, and turquoise occur only in one single color and are fairly color-constant. The chemical composition of the allochromatic stones, on the other hand, when pure, produces completely colorless specimens. Whence comes their color, then? Eight chemical elements—titanium, chromium, iron, nickel, vanadium, manganese, cobalt, and copper gold wedding bands—are characterized by an anomalous atomic structure.

They cause the absolutely astonishing display of colors by their "accidental yet arbitrary presence." These chromophorous (color-imparting) foreign substances crept into the mineral as dust-fine metallic clouds, but are so sparsely distributed that they can only be traced by the spectroscope, their average order of magnitude amounting to no more than 1-5 percent by weight. Think of it! 1-5 percent is sufficient to convert worthless into precious! The majority of well-known gemstones are thus "invaded." Moreover, depending on the yellow diamond rings host structure, one given coloring agent can provoke different colors, for example, chromium can produce ruby, spinel red, emerald, and demantoid green.

The incorporation of these foreign elements, which distort the host structure, produces electromagnetic fields of tension with free energies in the crystal lattice. Light, in its turn, is likewise a form of electromagnetic energy, that is, the sum of variously high energies. A given energy charge corresponds to a definite wavelength, which affects our eyes as color. The light falling on a colored gemstone suffers a loss of a certain energy component at the color centers, i.e., a selective absorption takes place. Now, only that mixture of colors which has not been absorbed emerges from the gemstone. In ruby the entire green component and the greater part of the blue component of light is absorbed, so that only a mixture of red, yellow, and a very little blue can emerge. These colors together produce the beautiful carmine red of ruby.