About Emeralds
Emerald is the green variety of beryl (Be3Al2Si6O18) coloured by trace amounts of chromium and, in some deposits, vanadium. It is one of the four traditional “precious” gemstones — alongside diamond, ruby, and sapphire — and has been mined and treasured for at least four thousand years; emerald cabochons have been recovered from Egyptian tombs of the Middle Kingdom, and Cleopatra's emerald mines near the Red Sea operated from the second millennium BCE until the time of the Roman Empire.
The premier source of fine emerald has been, since the sixteenth century, the deposits of the Cordillera Oriental in central Colombia. The Muzo, Chivor, Coscuez, and La Pita mines produce emerald of a distinct bluish-green hue and a quality of crystal seldom matched elsewhere; the very best Colombian material commands prices comparable to top-quality blue sapphire and ruby. Zambian emerald, mined at Kafubu and other deposits since the 1970s, runs darker and slightly more bluish than Colombian, often with greater clarity and a deeper saturation. Panjshir emeralds from the Hindu Kush of Afghanistan have entered the trade in significant volumes since the early 2000s and produce material of exceptional colour and remarkable clarity. Distinguishing Colombian from Zambian, Brazilian, or Afghan emerald is a core analytical task at every AGL laboratory.
Emerald is unique among the major gemstones in that virtually every commercial stone has been treated — not by heat, but by the application of oils and resins to surface-reaching fractures. Emerald crystals grow in geologically tumultuous environments and almost always carry visible internal fissures (the trade poetically calls these inclusions the stone's “jardin”). For thousands of years, lapidaries have impregnated these fissures with oils — traditionally cedarwood oil — to improve transparency. The modern trade additionally uses synthetic resins (Opticon, ExCel, and others) that offer greater optical match and longer-term stability but are more controversial.
AGL's emerald reports specify the type and degree of fissure filling using a four-tier scale: None, Minor, Moderate, Significant. This classification is supported by FTIR spectroscopy, which identifies the chemical signature of any filler present, and by microscopic examination under long-wave UV (synthetic resins typically fluoresce yellow-white). The use of green-dyed oils — an attempt to deepen the apparent colour of pale material — is treated as a separate, more serious disclosure on the certificate, as is any indication of fracture filling with epoxy resins that materially alter the appearance of the stone.
Origin determination on emerald draws on LIBS trace-element analysis (vanadium-to-chromium ratios, alkali content, and iron levels are particularly diagnostic), inclusion-pattern study (the “three-phase” inclusions of Colombian Muzo emerald, comprising a gas bubble and a crystal of halite within a brine-filled cavity, are virtually unique to that deposit), and UV-VIS-NIR absorption spectroscopy. For an emerald buyer, the AGL certificate confirms natural emerald species, declares the country of origin where analytically supportable, and discloses the degree of oil or resin treatment on a clear four-tier scale — the three pieces of information that together determine emerald value.
How AGL certifies Emeralds
Every emeralds submitted to an AGL laboratory is examined by at least two senior gemologists and analysed using our standard instrumental package: refractive-index and specific-gravity measurement, microscopic examination under dark-field and fibre-optic illumination, UV-VIS-NIR absorption spectroscopy, FTIR spectroscopy for treatment detection, and LIBS or ED-XRF for trace-element analysis where origin is in question. Every conclusion on the certificate — species, variety, treatment, origin — is supported by recorded analytical data, and every certificate is recorded in our secure verification database for online authentication at any time.
For full service descriptions and turnaround times, see our Services page, or contact your nearest AGL laboratory for a written quotation.
