Zambian Emerald

Buying this stone

Where it came from, what its weight band is for, and what to check before any money changes hands.

The deposit

The Kafubu field near Kitwe, of which the Kagem mine is the largest part, is schist-hosted, and the surrounding rock is rich in iron. Iron pushes Zambian emerald a step towards blue and a step darker in tone than Colombian material from Muzo, which grows in calcite veins and runs warmer and purer green. The trade-off is in the clarity: Zambian crystals generally reach the cutter with fewer fractures than Colombian ones, which is why a Zambian stone can often be sold with less filling in it than a Colombian stone of the same apparent clarity.

This stone

At 4.46 carats in an oval this is a ring centre, and it is above the weight where emerald pricing becomes noticeably non-linear. Emerald is a low-density stone compared with corundum, so it spreads: a 4.46 carat emerald covers appreciably more finger than a 4.46 carat sapphire and reads larger than its weight. That is worth knowing before you compare it on carats alone against a stone from a different species. Because it is a single stone rather than a parcel, the clarity you see is the clarity you get, with nothing to select from and nothing to average out.

Treatment

Essentially every emerald in commerce has had its surface-reaching fissures filled, and the grading scale for it runs none, minor, moderate and significant. That grade tells you more about what you are buying than the carat weight does. This stone is sold as unheated and untreated, which for emerald is a much stronger claim than the same words on a sapphire, and it is the claim to interrogate hardest on any emerald anywhere. Ask what filler a stone carries if it carries one: cedarwood oil can be redone by any workshop, hardened resin cannot be removed without risk to the stone.

The report

No report is held for this 4.46 cts emerald stone yet, and we would rather say that than name a laboratory that has not seen it. We will submit it to IGI or IIGJ before purchase on request.

Before you pay

• Look into the stone with a diffused light behind it and find the jardin. An emerald with no visible inclusions at an ordinary price is the warning sign, not the prize.
• Rock the stone under a point light and watch the fissures for a flash of a different colour, which indicates a filler with a refractive index that does not quite match.
• Check the girdle and any facet junctions for chipping. Emerald is brittle where it is fractured and this is where damage starts.

Read next

Panna, the emerald covers the material itself and what gets sold in its place. How to buy a coloured stone covers pricing, treatment and reports.

Written by Kamal Kishore Agarwal, founder and gemmologist, Gem-A qualified, buying in Johari Bazaar since 2008.