Why we are documenting Nigerian emerald cutting yield
Rough emerald is normally sold before the buyer knows exactly what the finished gemstone will weigh or look like. That uncertainty is where much of the risk — and expertise — lies.
A crystal can appear large but contain fractures that force it into multiple smaller stones. Another may be relatively modest in size yet contain one clean, strongly coloured block that produces an excellent finished gem. Professional cutters must continually trade weight retention against colour, transparency, clarity and durability.
Nigerian material adds another variable: documented colour zoning can be pronounced.
Our research method
Every research crystal should receive a permanent identifier before any cutting takes place:
NE-R001
NE-R002
NE-R003
The identifier should remain attached to all photographs, cutter records, finished stones and laboratory reports derived from that piece.
Before cutting, record:
| Field | What is recorded |
|---|---|
| Crystal ID | Permanent research identifier |
| Reported origin | Country and locality with evidence level |
| Rough weight | Grams and carats |
| Dimensions | Length × width × depth |
| Colour | Observed hue/tone/saturation and zoning |
| Transparency | Transparent, semi-transparent, translucent etc. |
| Fractures | Location and apparent severity |
| Inclusions | Major visible internal features |
| Predicted shape | Cutter/dealer's preferred finished form |
| Predicted yield | Estimated finished weight before cutting |
Photography standard
Each crystal should be photographed:
- against a neutral white background;
- against a dark background;
- with transmitted light;
- from the principal crystal faces;
- next to a scale or measurement reference where practical;
- after marking any planned saw lines.
Video should show the same crystal turning through 360 degrees. Consistency is more valuable scientifically than making every rough crystal look as attractive as possible.
Record every cutting decision
Before the saw touches the stone, record why a particular plan was chosen.
For example:
“Saw across central fissure to create two preforms.”
“Orient table to preserve the strongest green zone.”
“Accept lower weight retention to remove an open surface-reaching fracture.”
This is where the project becomes more useful than a simple before-and-after gallery. It explains why the weight disappeared.
GIA's observations of emerald manufacturing show that orientation for face-up colour, clarity, weight retention and treatment response are integral to planning valuable rough.
Calculating polished yield
Use one transparent formula:
Polished yield (%) = total finished carat weight ÷ original rough carat weight × 100
If a single crystal produces multiple gemstones, add the weights of every saleable finished stone derived from that original crystal before calculating total yield.
Keep secondary outputs separate:
faceted yield
cabochon yield
specimen retained
waste
That avoids artificially making a parcel look more productive by mixing fundamentally different outputs.
There is no universal emerald yield
Published trade examples demonstrate enormous variation.
GIA reported a highly fractured, colour-zoned 60 ct Afghan emerald rough that produced a 12.52 ct cushion — about 20.9% polished weight retention. GIA, 2016
In a separate rough-buying demonstration, Arthur Groom explained that crystal preservation and breakage can produce dramatically different yields. Those observations arose from Afghan material and should not be imported as fixed Nigerian percentages. GIA, Emerald Dealing in Afghanistan
The purpose of this project is specifically to discover what happens with documented Nigerian material rather than borrow yield assumptions from another origin.
Post-cut data
For each finished stone record:
| Field | Post-cut record |
|---|---|
| Finished weight | Carats |
| Dimensions | mm |
| Shape and cutting style | Emerald cut, cushion, oval etc. |
| Finished colour | Observed face-up colour |
| Transparency | Post-cut assessment |
| Major inclusions | Features retained after cutting |
| Treatment | Actual treatment/laboratory result |
| Laboratory identification | Emerald, green beryl or other result |
| Origin opinion | Where laboratory service supports it |
| Yield | Calculated from original rough |
Documenting laboratory results
Laboratory testing is particularly important where pale green Nigerian material sits near the emerald/green-beryl nomenclature boundary. GIA's recent Nasarawa Eggon research demonstrates that material containing iron, trace vanadium and chromium can still be identified as green beryl rather than emerald. GIA, New Nigerian Green Beryl Find
When a stone receives a report, publish the laboratory, report number where appropriate, variety identification, treatment conclusion and geographic-origin opinion exactly as reported.
From sourcing cost to finished cost per carat
Where commercially appropriate, the project can also record:
rough purchase cost
international shipping/import cost
cutting cost
laboratory cost
finished saleable carats
A useful business metric is:
total attributable cost ÷ total saleable polished carats = cost per finished carat
This should be kept separate from market value. Cost does not determine what a gemstone is worth.
Why publish failed stones?
Failures are arguably the most informative part of a rough-to-cut database.
A crystal that breaks, loses almost all its colour, proves too fractured to facet or is laboratory-classified as green beryl rather than emerald tells buyers something that successful stones alone cannot.
The objective is not to prove that Nigerian rough offers spectacular yields. It is to build a transparent record of what actually happens.
Current project status
At launch, this page documents the methodology rather than claiming results that do not yet exist. Results should appear only when individual Nigerian rough crystals have completed the relevant stages of documentation, cutting and — where stated — laboratory testing.
That distinction should remain explicit. The credibility of this research section depends on never filling an empty dataset with estimates presented as observations.