Andean Scapes team · Updated
Colombian vs Zambian emeralds: what is actually different
Zambia is Colombia’s biggest rival for fine emeralds. They form in different rocks, carry different traces and, in many stones, can still look alike. Here is what laboratories use to tell them apart.
The short answer
They form in different geological settings. Colombian emeralds belong to the hydrothermal/metamorphic group; Zambian emeralds from Kafubu are schist-hosted, formed where pegmatites or other magmatic bodies met mafic, ultramafic or metamorphic rocks.[1]
Zambia is one of the sources that, from the 20th century, challenged Colombia’s place in the market, alongside Brazil and Russia. As production spread, geographic origin became an important factor for fine emeralds.[1]
Different rocks, different ages
Colombian emeralds formed when hot basin brines, after interacting with evaporites, circulated through black shales rich in organic matter.[3] Zambia’s emeralds, like other schist-hosted deposits, formed instead where pegmatites or other magmatic bodies met mafic, ultramafic or metamorphic rocks.[1]
In Colombia the host is black shale: the western belt sits in rocks 130 to 116 million years old, and the emeralds formed about 65 million years ago in the east and 38 to 32 million years ago in the west.[3]
Color and iron
Schist-hosted emeralds such as Zambia’s tend to be a darker green than Colombian ones because they generally contain more iron.[1]
Trade lore says Colombian emeralds have a warmer, more intense pure green and Zambian ones a cooler, more bluish green. GIA notes that appearance overlaps between sources.[2]
Jagged versus blocky
Colombian emeralds typically show jagged three-phase inclusions; schist-hosted emeralds generally have blocky ones, and mica is their most common solid inclusion. Jagged inclusions larger than about half a millimeter are unique to Colombia.[1]
There is overlap at the edges: a minor Zambian deposit at Musakashi can show jagged three-phase inclusions similar to Colombian ones.[1]
How a laboratory decides
Origin is determined by combining inclusions, UV-Vis-NIR spectroscopy and trace-element chemistry measured by laser ablation ICP-MS.[1]
Iron shows up in the spectrum: schist-hosted emeralds have a much stronger iron absorption band at 810 nanometers. When a stone lacks diagnostic inclusions and trace-element data, an origin opinion may be impossible.[1]
Is Colombian better than Zambian?
Not automatically. Value depends on the individual stone: its color, clarity, cut and size. Appearance overlaps between sources.[2]
Origin does matter commercially: it has become an important factor for fine-quality emeralds.[1] But a fine Zambian stone beats a poor Colombian one; judge the stone, then ask a laboratory about its origin.
Frequently asked questions
- Are Zambian emeralds darker than Colombian ones?
- They tend to be. Schist-hosted emeralds like Zambia’s generally contain more iron, which makes them a darker green.[1]
- Can a laboratory tell a Colombian emerald from a Zambian one?
- Usually, by combining inclusions, spectroscopy and trace-element chemistry. Large jagged inclusions over about half a millimeter are unique to Colombia.[1]
Sources
- Saeseaw, S., Renfro, N. D., Palke, A. C., Sun, Z. et al. (2019). Geographic Origin Determination of Emerald. Gems & Gemology, 55(4). GIA.
- GIA Gem Encyclopedia. Emerald Quality Factors. Gemological Institute of America.
- Pignatelli, I., Giuliani, G., Ohnenstetter, D. et al. (2015). Colombian Trapiche Emeralds: Recent Advances in Understanding Their Formation. Gems & Gemology, 51(3), 222–259.