Gemologist Guide to Identifying Tsavorite Garnet

Tsavorite garnets are highly sought after by collectors and gemstone cutters because their beautiful green color and high dispersion make them perfect candidates for high-end jewelry. They’re composed of calcium aluminum silicate and the intense green color is caused by traces of chromium or vanadium.

They’re part of the grossular garnet family and the name comes from the area it was discovered; Tsavo National Park in Tanzania, along the borders of Tanzania and Kenya. It is reported that this is still the only place on Earth the precious gemstone is found.

 

 

How to Identify Tsavorite Garnet 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, then feel free to share it with us.

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

 

Visual Inspection

The visual inspection starts with what form of tsavorite garnet you have.  The questions below are fairly 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 medium to high polish with very little pitting on the surface. For years, you’d never see a tsavorite garnet in cabochon form but over the last couple of years, they’ve made their way into the gem dealers’ hands.

 

 

Is it faceted? If you have a faceted piece of tsavorite garnet, then it should be transparent and you should assume there will be natural inclusions. You’ll need to use a 10x powered loop or microscope to view the interior of the stone. Feathers, clouds, and included crystals are fairly common for this garnet. Most faceted stones are sub 3 carats but you will see large rare stones with high clarity from time to time.

 

 

Is it a specimen? Tsavorite garnet is found in different forms, and you’ll get better at identifying these forms by looking at and inspecting this mineral over time. Here’s a list of characteristics tsavorite garnet displays when it’s a specimen.

• Translucent to semi-transparent.
• Rich green natural colors with some graphite and pale blue-gray surrounding it.
• You’ll be able to do the streak test; keep reading below if you have a rough piece with no commercial value.
• It can be found in crystal form, but it’s rarer, and you’re not likely to come across it very often.  These crystals are typically on the smaller side and considered to be micro-specimens.

 

Is it tumbled? You could come across low-quality tsavorite garnet that has been tumbled or made into beads.  Again, metallic shine with very little pitting.  Mint green to dark green colors with streaks of earthy colors like brown, cold, and touches of silver.

 

Physical Properties of Tsavorite Garnet

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

 

Color: Bright Yellowish Green, Green to Emerald green

Clarity / Transparency: Transparent to Opaque

Luster: Vitreous to Resinous

Cleavage: Indistinct

Fracture: Conchoidal, Somewhat Brittle

 

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 is when you scrape the stone against a harder surface to see what color remains.

Raw Tsavorite Garnet can be streaked across a piece of colored paper to expose its color. Tsavorite garnets are always white.

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

 

Magnet Test

Garnets are among the only common transparent gemstones that produce a Pick-Up response to N52 magnets. They’re more magnetic than other transparent stones because they typically contain higher concentrations of paramagnetic iron, with measurements up to 35 percent iron oxide by weight. They also contain higher concentrations of manganese, up to 40 percent manganese oxide by weight.

However, the magnetic attraction will vary depending on the type of Garnet. For example, Spessartite contains is the most magnetic, while Tsavorite Garnets are on of the least.

 

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, Tsavorite Garnet has a hardness of 6.5 to 7.5 on the Mohs hardness scale.

 

Refractive Index Test

Determining the refractive index, or RI as it’s referred to by gemologists, for tsavorite garnet is fairly 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.

 

Tsavorite Garnet’s Refractive Index: 1.734 – 1.759

 

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 of the gauge.

 

Birefringence Test

You won’t be using this test for tsavorite garnet, but I wanted to include this test just in case you were considering it in your process.

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: 0.000 – 0.005

 

Single or Double Refraction

Tsavorite Garnet is singly refractive.

You won’t need this test for Tsavorite Garnet, but I wanted to include this test just in case you were considering it in your process. 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 light and stays light, it is likely AGG. If the lightness or darkness of the stone changes, it is likely DR.

 

Checking The Diaphaneity

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

Tsavorite Garnet is transparent to translucent. However, its translucency depends on the form it has taken. If the Tsavorite Garnet 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.

 

Tsavorite Garnet’s Specific Gravity: 3.60 – 3.68

 

As helpful as specific gravity is for identifying minerals, amateurs are usually constrained by the lack of necessary tools for the job. 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, then 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 your practice to identify a piece of tsavorite garnet 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 get confused, then feel free to reach out. I’ll do my best to assist you in the identification process.