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Identifying Rough Diamonds
Identifying Rough Diamonds

Identifying Rough Diamonds

Due to their incredible durability and sparkling beauty, diamonds are one of the most sought-after gemstones in the world. While it's easy to recognize a cut diamond, however, not many people would be able to tell whether an uncut or raw diamond is the real thing or not.

Uncut rough diamonds look very similar to water-worn quartz pebbles. However, there are other rocks that can be mistaken for raw diamonds by people who do not know how to spot the precious material. Luckily for people who want to learn how to identify a raw diamond, there are various ways to identify a raw diamond with a high degree of certainty.

If you think you have a rough diamond or think you have found a diamond. This guide will tell you how, and how not to identify rough diamonds as they are found in nature.

The chances of finding a rough diamond are extremely rare. Odds are you did not find a diamond. First a few questions:

1. Is the suspected diamonds larger than 8 mm (3/8 of an inch)?

2. Does the suspect diamond weigh more than 2 grams (10 carats)?

3. Did you find more than one suspected diamond?

If the answer to any of the above questions is YES, then you probably don't have a diamond or did not find a diamond.

Diamonds over 8 mm, in excess of 2 grams in weight are extremely rare. The chances of finding a diamond are 1 in 10,000,000. The chances of finding a diamond over 8 mm, in excess of 2 grams in weight are 1 in 1,000,000,000. That is one chance in a billion!

Rough Diamonds

Rough Diamonds.

OK, so you think you beat the odds and actually found a rough diamond. Now how do you test it to confirm it is a diamond?

Crystal Form:

Looking at the crystal form is a quick way of differentiating diamond from most of the other minerals that look like diamond.

Crystal Form

Crystal Form.

Diamonds are cubic (isometric) form. The most common mineral that looks like a diamond is quartz and it is hexagonal form. When looking down on the crystals from the top, with the point of the crystal aimed at your eye, quartz will have six sides and a diamond will have four sides. If you see six sides than you probably found quartz.


When diamonds break, they will cleave creating smooth, flat surfaces. Quartz and glass will create conchoidal surfaces when they break.



If you see curved conchoidal surfaces (see photo above) then you know your sample is not a diamond.

Test Hardness:

You can not test the suspect diamond by scratching glass.

Many minerals scratch glass. Glass is 5.5 on the Moh's Scale of Hardness. The following list is of common minerals that scratch glass, may look like diamonds and they are much more common than diamonds:

Albite Grossular Quartz
Beryllonite Marialite Sanidine
Boracite Oligoclase Sillimanite
Corundum Orthoclase Spodumene
Danburite Petalite Topaz
Elbaite Phenakite Zircon
Euclase Pollucite Zoisite

So do not try scratching glass with the suspected diamond. The only hardness test that will identify a diamond is scratching corundum. Corundum, which includes all rubys and sapphires, is 9 on the hardiness scale. If your suspected diamond crystal can scratch corundum, then there is a good chance that you found a diamond. But no other hardness test will identify a diamond.

Test for Thermal Absorption:

Diamonds absorb heat better than any other mineral and there are a wide variety of portable diamond testers on the market.

Test for Thermal Absorption

Test for Thermal Absorption.

These diamond testers are hand-held devices with a metal probe that is held in contact with the suspected diamond. It generates a small amount of heat and measures the speed that the heat is absorbed by the crystal. Good testers can differentiate between diamond, moissanite (a common synthetic diamond-simulant), and other minerals.

You do not have to buy a diamond tester. Almost any reputable jeweller will own one, and testing is quick and easy. So try visiting your local jeweller and ask if he will test your suspected diamond.

Specific Gravity

Those who want to know how to identify a raw diamond would be remiss not to learn about specific gravity. Simply put, specific gravity is the ratio that exists between the density of a gemstone and a reference liquid. Typically, this liquid is pure, distilled water, a liquid that has a density of 1 g/mL.

Diamonds have a specific gravity of 3.1 to 3.5. In comparison, quartz has a specific gravity of 2.6 to 2.7. By learning what the specific gravity of a gemstone is, it is possible to know with certainty whether it is a raw diamond. This property of diamonds also serves as a way to separate them from other gemstones using shaker tables or similarly purposed tools.

Microscope Test

Often, people who want to know how to identify a raw diamond are glad to find out it is possible to do this just by looking at the stone. However, it is also necessary to use a 10x power jeweller's loupe or, even better, a microscope. There are two main things to look for when trying to identify a diamond. The first is its appearance; under the microscope, diamonds look as if they had been coated with a thin film of Vaseline. The second thing to look for is certain markings such as indented triangles, parallelograms or rotated squares.


The odds are against you finding a diamond. But if you are not convinced, first look at the crystal shape to see if it is isometric form, make sure the fracture surfaces are not conchoidal, check if it scratches a corundum crystal. If it passes all of the above, then try a diamond tester to measure thermal absorption.

Final thought

The odds of finding a diamond are equal to being struck by lightning on your birthday 20 years in a row. Even if you found a real diamond, purchased a diamond tester to verify, nobody will take you seriously. The ONLY way you will convince anybody it is a real diamond is to have it certified by the Gemmological Institute of America (GIA). For a fee they will test your "diamond" and give you a certificate absolutely, positively identifying it as diamond, plus they will give you back the diamond unharmed. With that certificate you will have proof of your find, and buyers will be seriously interested in purchasing your find.

Because a GIA certificate will eventually be required anyway, save your money and do not buy a diamond tester. Instead send it straight to the GIA for a certification.