Colombia, the world’s largest supplier of emeralds
While emeralds in ancient times were mined in Egypt, India and Austria, the best and most famous emeralds are found in two renowned mines in Colombia – now the world’s largest supplier of emeralds, responsible for more than 60 percent of global production. Other major suppliers include Brazil, Zambia and Zimbabwe.
The first of Colombia’s most famous mines, Chivor – named after the Chibcha people who once owned the land – was opened under Spanish control in 1537. Thirty years later, the most prolific emerald mine in history was discovered 60 miles north of present-day Bogotรก: Muzo.
Muzo yielded some of the most famous emeralds in history, including the Devonshire – an uncut stone weighing a massive 1,383.95 carats, named after the 6th Duke of Devonshire, who received it from Emperor Dom Pedro I of Brazil.
The importance of color, clarity and saturation
When evaluating gemstones, color is usually the most important criterion – although in the case of emeralds, clarity ranks second. The most desirable stones have both a luscious green hue and a high degree of transparency.
For a stone to be considered an emerald, it must have a medium to dark hue – with stones with a lighter hue known by the generic name green beryl. A high saturation of green is also highly desirable.
Inclusions and blemishes
A natural occurrence for emeralds is the presence of inclusions and cracks on the surface – in fact, this is so common for emeralds that a “clean” stone is virtually unknown. Jewelers call these inclusions jardin, or garden, because they are said to resemble a moss-covered wilderness “growing” inside the stone.
Use of oils and polymers
Most emeralds are treated in some way, to fill surface cracks, improve clarity and sometimes stability. Common treatments include the use of oils and polymers.
Because the treatment is so common, it is classified on a four-level scale: none, insignificant, minor, moderate and significant. Although it is accepted, the degree of treatment can lower the value: untreated emeralds of similar appearance would take a much higher value, due to their exceptional value.
Rectangular step cut, beads and cabochon cuts
Emeralds can be cut in a variety of ways, the most popular of which is the rectangular stepped cut, commonly known as the “emerald cut.”
Bead and cabochon cuts are also popular. Unlike facet cuts – which are geometric in form – cabochons are gemstones that have been shaped and polished, usually resulting in a rounded shape with a flat reverse.
Source: https://www.christies.com/features/collecting-guide-emeralds-9906-3.aspx?sc_lang=en