The ruby is one of the most celebrated and valuable colored gemstones, instantly recognizable as a brilliant, deep red jewel. This familiar appearance is the result of skilled craftsmanship and intensive labor. To understand a ruby’s origin, one must consider its raw state, deep within the earth, where it appears far less glamorous than the finished jewelry.
The Mineral Foundation
The ruby is scientifically defined as the red variety of the mineral corundum, which is aluminum oxide. Pure corundum is naturally colorless, but trace elements determine its final hue. The characteristic red color is caused by small amounts of chromium substituting for aluminum atoms during the crystal’s formation.
The intensity of the red color is directly related to the concentration of chromium present. Rubies form under intense heat and pressure in two primary geological settings. They are found in primary deposits embedded within host rocks, such as metamorphic marble or basalt, or they are located in secondary placer deposits, having been weathered free from their original source rock into riverbeds and gravels.
The Appearance of Uncut Rubies
A freshly mined ruby does not possess the sparkle or the intense, uniform color commonly associated with the gem. Instead, it is typically found as a rough, often lumpy, crystal that is opaque or only partially translucent. The crystal habit of corundum often manifests as a six-sided, or hexagonal, prism shape, sometimes appearing barrel-shaped with dull, striated faces.
The surface of the stone is usually not reflective but rather dull, greasy, or earthy in appearance, often covered in a layer of dirt, clay, or remnants of the surrounding matrix rock. When found in primary deposits, the ruby crystal is embedded within the host rock, where it often looks like a reddish-pink inclusion rather than a distinct, standalone gem. Even the color is muted, appearing as a dark pinkish-red or a brownish-red, far removed from the vibrant, pure red hue of a finished stone.
The color within the rough stone may also be unevenly distributed, showing distinct color zoning or patchy areas. Natural inclusions, such as fine needles of rutile known as “silk,” are common within the rough material, reducing its clarity and making the stone look cloudy. These features, coupled with the dirty, non-reflective exterior, make the rough stone look unremarkable to the untrained eye and require significant effort to evaluate its potential.
From Rough Stone to Polished Gem
The journey from a rough crystal to a polished jewel begins with careful washing and cleaning to remove the adhering dirt and matrix material. Once cleaned, the gem cutter, or lapidary, must meticulously study the rough stone to determine the best orientation for cutting. This decision is crucial because the final color and brilliance depend on how light will travel through the crystal’s structure.
The cutter must plan the process around the stone’s inclusions and color zoning to maximize the yield and beauty of the finished gem. Given the ruby’s high hardness—a nine on the Mohs scale—specialized equipment, such as diamond-coated saws and grinding wheels, is required for shaping and faceting. Faceting involves creating numerous flat, geometrically arranged surfaces to maximize the stone’s light return and internal fire.
The final stage is polishing, where the stone is buffed with increasingly finer abrasive pastes, often using diamond powder, until a high-gloss luster is achieved. This polishing step transforms the once-dull, rough crystal surface into the brilliant, reflective gemstone recognized in jewelry. The inherent hardness and stability of the corundum crystal allow it to withstand this rigorous process and maintain its final, intensely red form.