Emerald

Emerald is a gemstone and a variety of the mineral beryl (Be₃Al₂(SiO₃)₆) colored green by trace amounts of chromium and sometimes vanadium. Beryl has a hardness of 7.5–8 on the Mohs scale. Most emeralds are highly included, so their toughness (resistance to breakage) is classified as generally poor. Emerald is the birthstone for May.

Formation & Geology

Emeralds form in hydrothermal veins or pegmatites. The formation of emerald requires a unique geological environment where beryllium (from granitic magmas) comes into contact with chromium or vanadium (typically from ultramafic rocks). This specific combination of elements is geologically rare. The finest emeralds are found in Colombia, where they occur in sedimentary host rocks.

Physical Characteristics

Emeralds are known for their rich green color. Unlike other beryls, emeralds often contain inclusions and surface-breaking fissures. These are so common that they are considered part of the stone's character, often referred to as 'jardin' (French for garden). Because of these inclusions, emeralds are often oiled to fill fissures and improve clarity. While they are hard minerals, their internal stress makes them brittle.

Historical Significance

Emeralds have been cherished since antiquity. The first known emerald mines were in Egypt, dating from at least 330 BC into the 1700s. Cleopatra was known to have a passion for emeralds and used them in her royal adornments. The Incas had been using emeralds in their jewelry and religious ceremonies for 500 years before the Spanish arrived.

The "Oil" Treatment

Because emeralds naturally contain many fissures and inclusions, over 99% of them are treated with cedar oil or synthetic resins (like Opticon) to fill these gaps. This improves clarity and stability. It is vital to never clean emerald jewelry in an ultrasonic cleaner, as the vibrations can shake the oil out, making the inclusions visible again or even cracking the stone.