Identifying Scapolite can be difficult because it is easily confused with Citrine and Amethyst. In its crystal form it’s fairly simple to accurately identify it but when it is faceted the difficulty level increases considerably.
If you want to get good at identifying Scapolite quickly then you’ll need time with the rough and faceted stones while comparing side by side to Amethyst and Citrine. I do my best to explain the major visual difference below and I hope you enjoy it.
While Scapolite isn’t one of the well-known gemstones, it’s an attractive gem material for mineral collectors and jewelry enthusiasts. These stones come in a variety of colors and can show dramatic fluorescence. Rare Scapolite specimens display chatoyancy.
How to Identify Scapolite Through Testing
There are various ways to identify rocks, minerals, crystals, and gemstones, but we will use a method I learned while attending the Gemological Institute of America. If you’ve learned a unique way to identify gems, please share it with us.
Let’s look deeper into how to identify Scapolite like a pro.
The visual inspection starts with what form of Scapolite you have. The questions below are relatively easy to answer, but each type will have its own process for identifying them.
Scapolite comes in two distinct colors, yellow and purple.
Purple Scapolite will look watery or have grey undertones.
Yellow Scapolite will have a medium to light yellow color with no orange undertones. If you look closely you’ll see grey mixed in with the yellow.
Is it a cabochon? On occasion, you will come across small batches of Scapolite cabochons but they are not common. More than likely they will have some inclusions and a high polish. If you are looking at a cabochon then I would err on the side of Amethyst but continue to work your way through the testing protocol to ensure accuracy.
Is it faceted? It is fairly common to see faceted purple and yellow Scapolite at a gem show but you probably won’t see it at your local jewelry store. The biggest tell will be the washed-out color with grey undertones. Try setting it next to a faceted Amethyst if you need help spotting the washed-out color and greys.
Is it a specimen? Scapolite 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 Scapolite displays when it’s a specimen.
- Scapolite’s host rock can be Schist, Gneiss, or Marble.
- Under short-wave and long-wave ultraviolet lights, Scapolite will fluoresce from yellow to orange.
- Specimens can have a wood-grain or fibrous texture.
- Scapolite can have inclusions of irregular-shaped black platelets or discoids.
Is it tumbled? It is not very common to see tumbled Scapolite but you will come across batches of low-grade material that can be tumbled.
Physical Properties of Scapolite
Let’s take a look at the physical properties of Scapolite. Knowing what to look for will help you more easily identify what you’re looking at.
Color: Yellow, Purple, Gray
Clarity / Transparency: Transparent, Opaque
Fracture: Conchoidal, Brittle
The Streak Test
This is a destructive test, so you must ensure that you can damage the specimen or stone if you choose to use this method. You won’t use destructive tests once you’ve developed robust knowledge in identifying rocks and minerals.
A mineral streak test is when you scrape the stone against a harder surface to see what color remains. Scapolite always produces a white streak.
Tumbled specimens are tested by scraping samples across a piece of ungalvanized porcelain, typically known as a streak plate.
Scapolite has a very weak attraction to strong magnets.
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. Scapolite has a hardness of 5 to 6 on the Mohs hardness scale.
Refractive Index Test
Determining the refractive index, or RI, as it’s referred to by gemologists for Scapolite, is relatively straightforward. Still, 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.
Scapolite’s Refractive Index: 1.54 – 1.58
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.
Occasionally, 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 can pull a reading off of the gauge.
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: 0.015 – 0.020
Single or Double Refraction
Scapolite displays a double refraction.
The stone must be transparent for this test to be accurate and beneficial. If the light won’t pass through the stone, 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 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.
Scapolite is transparent to translucent.
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.
Scapolite’s Specific Gravity: 2.5 – 2.7
As helpful as specific gravity is for identifying minerals, amateurs are usually constrained by the need for more 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, you’ll need to invest in a higher-end scale. The OHAUS Density Determination Kit is the one gemologists use.
Identifying Rocks and Minerals Like a Pro
Hopefully, you feel confident in your practice of identifying a piece of Scapolite 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.
Feel free to reach out if you encounter any issues or need clarification. I’ll do my best to assist you in the identification process.