A Cutter's Guide to Evaluating Rough Emerald Parcels

Emeralds are rulebreakers in the world of gems because fractures don't make or break the gem's value. You can pit two stones against each other, and their values could be very different, especially if you factor in where they come from. Most analyses also happen in dim lighting under a loupe, not in the lab. Here, you'll learn how to evaluate rough emeralds and what makes them valuable before you make the first cut.

1. Build the Kit Before You Open Anything

1. Minimally, use a 10x loupe: try to get 10x or 20x. Some like bench microscopes too to look at the feather fractures.
2. Tiny pens/fiber optic lights: indoor lights make stones look Overhead lighting flattens a stone's interior. Light run along the length of the crystal at an angle reveals fracture planes and color zoning that flat light hides completely.
3. A gram scale accurate to 0.01g.A gram scale to the hundredth of a gram gives an exact estimate of the weight of a stone. 
4. Calipers these help tell you the size of a stone. Help in judging how a rough shape maps onto standard finished proportions.
5. UV lamp, either a short-wave or long-wave lamp works to help you look for any odd fluorescence, which could lead you to finding out if a stone of synthetic. 
6. A Small Immersion Cell- Shot glass and clear liquid. 
7. A neutral gray or white cloth. Gray or neutral cloth to help determine the color of the stone. 
8. Notebook/spreadsheet to help log the stone’s weight, price, and any oddities you might see.

2. Establish Treatment Status Before You Judge Anything Else

Before doing anything else, determine whether the stone is rough or finished with a carry oil, resin, or wav to improve clarity. 

To check this: 

• Look at the fractures under light with the loupe. Oil tends to look a little rainbow when present in fractures. 
• Dab a cotton swab with acetone and press it to the fractures. This will lift any color changes or residues left behind. Don’t use this on high-value material, for it could ruin the piece. 
• Put the stone in the immersion cell, then under normal light. If the stone looks worse when reflected on the surface, that’s a treated stone 

Remember, this is your first step if you suspect treatment. If you’re looking to verify, get a lab report.

3. First Pass: Spread the Stones, Don't Judge the Pile

Spread out your stones.   Less valuable stones tend to look better against higher-value stones because the colors can reflect off each other, inappropriately gauging the price of a pile. 

Grab your cloth and spread out the parcel, looking at every stone. Try to separate each of them based on clarity and color, estimating the percentage of the weight within each type. 

If the parcel is about 15% a saturated green against 85% pale, that’s a very different price than one that’s split even down the middle, even if the stones look “typical.” Remember, look at every category as its own tier, not just on what crystal is the prettiest. The whole lot has to be judged when you’re getting stones.

A parcel to study

Once the stones are separated, a natural rough parcel makes it easier to compare color spread, surface character, and potential cutting yield.

Review a natural Swat rough emerald parcel

4. Read the Crystal Itself: Habit, Skin, and Core Color

Rough stones are usually priced on where they came from, but there are other factors to consider too. 

Primary vs. alluvial material. When you buy from a primary deposit, it has a glossy face to it, and you can see deep inside without a loop. Rough that’s a bit more weathered out, called alluvial deposits, look more frosted and sugary on the surface, but look opaque to the naked eye.   Alluvial material can bet wetted with oil or water to look at the crystal under the surface prior to cutting.

Use windowing. With emeralds and more fragile stones, you have to be more careful when mapping inclusions, so they don’t break. You have a couple of ways to check these more fragile stones. First, grind out a tiny window on these crystals that someone won’t see.  You can also put the stone in the immersion cell with water or a mineral oil. This will get rid of the glare to see the Jardin inside and how dense they look. 

Beware of the color risk. Crystals may look solid and saturated, but may look more washed out near the center of the stone.  Afghan stones tend to suffer from this. This does affect the color and attractiveness.   Before cutting, check right down the crystal’s length instead of right across. If the color remains nice and steady from beginning to end, then you’ve got a vivid stone. If it’s only vivid at the edges, you’ll know the color is washed out.

5. Estimate Emerald Cutting Yield Like You Mean It

Most stones yield up to 40% when cutting, but can drop up to 15% if there’s a Jardin or major fracture that’s running along the center. Knowing if a stone if fractured or complete, and if the color remains constant, will help you determine rough emerald value.

It’s important to use math before pricing a stone instead of just saying “it depends.”

To do this

1. Weigh the total parcel in carats (grams multiplied by 5). 
2. Use a conservative estimate of the yield percentage you might lose. 
3. Divide that initial cost by the estimated carats of the finished piece. This gives the true number of what you’re getting in carats.
4. Compare the math that you’ve done to what as stores are selling the finished sizes for to see if it’s worth buying. 

If you find yourself in the red by the time you get to step four, then it’s not worth buying.

From rough to finished

A finished loose emerald offers a useful visual counterpoint when you’re estimating how rough color, clarity, and yield may translate after cutting.

Study a vivid green Swat emerald loose gem

6. Red Flags: Synthetics, Imitations, and Re-Treatment

Here are things to watch out for when buying rough stones: 

• Coated fakes. These are stones that are just colored glass, with a coating that looks like a crystal in color and texture. These are beginning to show up a lot in parcels, so be mindful when buying. 
• Synthetic and rough parcels mixed. There is nothing wrong with synthetic and flux-grown emeralds, but some sellers mix them in with natural stones. Seeing the difference without deep magnification is hard, but if you see a stone that looks too perfect, or without any inclusions in any stone period, you might want to check to make sure it’s not synthetic. 
• Certificates don’t match the stone. A stone might be reported one way on the certificate, but it later has oil or resin, which means the verification and testing were not updated for fillings.  Some stones can also have their oil and resins removed. Stones can change, so ask for an updated report prior to buying. 

This isn’t always done maliciously, so make sure that, if you do see these red flags, bring them to light.

7. Understand the Grading Gap Between Mine and Market

There is a gap in how a stone is graded, especially when you compare auction house pieces, large-scale sellers, or even a smaller parcel that you can get from a mine-site broker. It does vary, because they usually tend to grade things very different, with discrepancies even in color and the shape of a stone. 

Be smart and use your judgment, creating your own system of tiers of stones. 

If you see a price that sellers are using, such as a gram, by the piece, or wholesale, make sure that this is consistent.   Cost per carat is best for rough pieces, but if you want to look at them in grams, do the match prior to committing to the sale.

Keep researching origin

Want a second perspective on origin, quality, and value? Continue with this practical comparison of two important emerald sources.

Read the Swat and Panjshir emerald comparison

8. The Paperwork Nobody Mentions

There are permits for exports, documentation for royalty, and other paperwork that comes with buying stones, especially from Columbia, Brazil, Zambia, and Afghanistan.   This can affect whether you can legally take the stone back to your home country.

Customs may also invoice you before the stone touches the country of destination, and must be declared as something that’s goods instead of a personal effect. 

Suppliers that don’t do the paperwork are a huge red flag and can get you in legal trouble. Some producers may also lie about the country of origin, while others are able to offer tracking of the stone once it leaves the mine.

Make sure you work with sellers that give you the upfront information on documentation, and don’t just claim where a stone is coming from.

The Parcel-Evaluation Checklist

1. Make sure the stone hasn’t had treatments that aren’t reflected on the paperwork. 
2. Spread out the stones on a neutral or white sheet. 
3. Sort the stones based on color and quality, while also estimating the weight percentages for each 
4. Find the alluvial and primary material, preparing as needed. 
5. Check the core color along the crystal’s length. 
6. Use a window or immersion cell to look for Jardins or fractures. 
7. Find out the yield per tier of stones instead of just the parcel. 
8. Once you have the grams, convert them to carats, find out the total yield, then the cost per carat of the lot before comparing prices 
9. Screen for any red flags, such as synthetic materials or imitation stones 
10. Ensure that documentation and requirements for export paperwork are finished before closing the deal. 

Buying a lot of stones can be a challenge, but if you’re aware of what you’re buying, you can buy high-quality pieces with little to no trouble.

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Further Reading

GIA's Gems & Gemology "Gem News International" archive includes first-person accounts of rough emerald buying, including sourcing trips to Afghanistan's Panjshir Valley. Gemfields publishes details of its own sorting and grading process for Zambian and Mozambican production. The International Gem Society's lapidary section covers general rough-buying, yield estimation, and synthetic-rough identification for other gem materials in more depth.

About the author: Samina Gulzar is the author of this article.

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