Gemologist Guide to Identifying Chyrsoberyl

Chrysoberyl is sought after by gemstone and specimen collectors because of its vibrant colors and unique crystal structure. During my time at the jewelry store, I rarely saw a faceted chrysoberyl, and the local rock and mineral shows don’t have a plethora of natural crystals.

If you have the opportunity to see and hold a natural chrysoberyl then it will probably be yellow or yellowish-green.

 

 

How to Identify Chrysoberyl Through Testing

There are various ways to identify rocks, minerals, crystals, and gemstones, but we will be using a method I learned while attending the Gemological Institute of America.  If you’ve learned a unique way to identify gemstones, feel free to share them with us.

Let’s take a deeper look into how to identify chrysoberyl like a pro.

 

Visual Inspection

The visual inspection starts with what form of chrysoberyl you have.  The questions below are relatively easy to answer, but each type will have its own process for identifying them.

 

 

Is it a cabochon? If you’re dealing with a cabochon, then it should have a medium to high polish with very little pitting on the surface.  The most common color will be yellow or yellowish-green and it will probably display a chatoyant effect, also known as cat’s eye chrysoberyl.

 

 

Is it faceted? If you have a faceted piece of chrysoberyl, it should be translucent. When the gemstone is faceted, it typically has a honey-gold to green color. It may appear similar to a yellow Sapphire, Tourmaline, Citrine, or Topaz.

 

 

Is it a specimen? Chrysoberyl is found in different forms. You’ll better identify these forms by looking at and inspecting this mineral over time. Here’s a list of characteristics chrysoberyl displays when it’s a specimen.

• Specimens can be yellow-green, greenish-yellow to golden brown
• It shows multiple twinning or trilling.
• It can be found in crystal form, but it’s rarer, and you’ll likely come across it infrequently.  These crystals are typically on the smaller side and considered to be micro-specimens.
• V-shaped twinning.
• Semi-transparent to transparent.

 

Is it tumbled? It’s not very common to find tumbled chrysoberyl but don’t get confused with alluvial pieces sold as faceting rough.

 

Physical Properties of Chrysoberyl

Let’s take a look at the physical properties of chrysoberyl. Knowing what to look for will help you more easily identify what you’re looking at.

 

Color: Shades of Green – Emerald Green, Yellowish Green, Greenish White, Greenish Brown, Blue, Yellow

Clarity / Transparency: Transparent, Translucent

Luster: Vitreous

Cleavage: Distinct / Good

Fracture: Irregular, Uneven, Conchoidal

 

The Streak Test

This is a destructive test, so you need to ensure that you’re allowed to damage the specimen or stone if you choose to use this method.  Once you’ve developed robust knowledge in identifying rocks and minerals, you won’t be using destructive tests.

A mineral streak test involves scraping the stone against a harder surface to see what color remains.  When dealing with chrysoberyl, you’ll notice a white streak.

Tumbled specimens are tested by scraping a specimen across a piece of ungalvanized porcelain, typically known as a streak plate.

 

Magnet Test

Chrysoberyl is only slightly magnetic, so it may or may not respond to a magnet.

For instance, it’s entirely normal for chrysoberyl to contain small amounts of iron. Iron ore is naturally magnetic, which is the main reason it might respond to a magnet. However, magnetic attraction ranges from weak to moderate.

 

Hardness Test

I don’t recommend actively testing the hardness of a stone because it’s destructive in nature and doesn’t really provide a definite answer to what type of stone it is.  With that being said, Chrysoberyl has a hardness of 8.5 on the Mohs hardness scale.

 

Refractive Index Test

Determining the refractive index, or RI as it’s referred to by gemologists, for chrysoberyl is relatively straightforward, but you’ll need a specific piece of test equipment and the RI fluid to go with it.  Before you place the stone on the refractometer, you want to make sure you have a flat, somewhat polished surface to take a reading.

 

Chrysoberyl’s Refractive Index: nα = 1.746 nβ = 1.748 nγ = 1.756

 

Each gemstone has its own RI, so discovering a sample’s RI can help you figure out what sort of stone it actually is.

Step 1 – Place a small bead of RI fluid on the metal surface of the refractometer near the back of the crystal hemicylinder (the window on which the stone will sit).

Step 2 – Place the stone facet face down on the fluid dot and slide it toward the middle of the hemicylinder crystal using your fingers.

Step 3 – Look through the viewer lens without magnification. Continue looking until you see the outline of a bubble, then look at the bottom of this bubble. Take the reading from there, rounding the decimal to the nearest hundredth.

From time to time, you’ll run into the issue of not having a flat surface to work with.  In this instance, you’ll need to leave the top of the refractometer open and hold the rounded stone with your hand.  Hopefully, you’ll be able to pull a reading off the gauge.

 

Birefringence Test

Chrysoberyl has a 0.010 birefringence which produces biaxial optics.

Consider testing the birefringence, as well. Birefringence is related to RI. While doing the birefringence test, you will turn the gemstone on the refractometer six times throughout the observation period and note the changes.

Perform a standard RI test. Instead of keeping the stone still, gradually turn it 180 degrees, making each separate turn about 30 degrees. At each 30-degree mark, take a new RI reading.

Subtract the lowest reading from the highest to find the stone’s birefringence. Round it to the nearest thousandth.

 

Birefringence: δ = 0.010

 

Single or Double Refraction

Chrysoberyl has a double refraction.

For this test to be accurate and beneficial, the stone needs to be transparent in nature.  If the light won’t pass through the stone, then there is no way to test for single or double refraction.

Check for single or double refraction. Use this test on translucent and transparent stones. You can determine whether the stone is only singly refractive (SR) or doubly refractive (DR) to help identify it. Some stones can also be classified as aggregate (AGG).

Turn on the light of a polariscope and place the stone face down on the lower glass lens (polarizer). Look through the top lens (analyzer), turning the top lens until the area around the stone looks darkest. This is your starting point.

Turn the analyzer 360 degrees and watch how the light around the stone changes.

If the stone appears dark and stays dark, it is likely an SR. If the stone starts out light and remains light, it is likely AGG. If the stone’s lightness or darkness changes, DR is likely.

 

Checking The Diaphaneity

Diaphaneity refers to the mineral’s ability to transmit light. For instance, some minerals are transparent or translucent. When they’re thick, a small amount of distortion might occur, but light will pass through them relatively freely.

Chrysoberyl is transparent to translucent. However, its translucency depends on the form it has taken. If the chrysoberyl has an earthy form, there won’t be much light traveling through it. Still, if it happens to take on a crystalline structure, you should expect an opaque diaphaneity.

 

Finding The Specific Gravity

Every stone has its unique specific gravity, which helps us identify them. Specific gravity is one of the best properties to measure when identifying mineral specimens. Most minerals have a narrow range of specific gravity, so getting an accurate measurement can go a long way toward identification.

Specific gravity is a unitless number describing how heavy a mineral is compared to equal volumes of water. For example, if a mineral is three times as dense as water, it’ll have a specific gravity of three. This is useful because while two minerals might be the same size, they’ll each have a different specific gravity.

The larger the sample, the more precise the readings tend to be. Remember that this technique can only be used for single mineral or crystal masses. It will not work for minerals embedded in host rocks.

 

Chrysoberyl’s Specific Gravity: 3.75

 

As helpful as specific gravity is for identifying minerals, amateurs are usually constrained by the lack of necessary tools. However, one way to work around this is to hold the specimen and note how heavy or heft it feels compared to what you might expect a specimen of that size to weigh.

If you want to determine the specific gravity of your stone like a pro, you’ll need to invest in a higher-end scale.  This is the one gemologists use OHAUS Density Determination Kit.

 

Identifying Rocks and Minerals Like a Pro

Hopefully, you feel confident in identifying a piece of chrysoberyl after reading and applying this guide.  You’ll be using the visual part of this guide the most, and you’ll get better as you interact with more gemstones.  Before you know it, you’ll be identifying stones like a gemologist.

If you run into any issues or you need clarification, then feel free to reach out, and I’ll do my best to assist you in the identification process.