Gemologist Guide to Identifying Barite

Barite often occurs as concretions and void-filling crystals in sedimentary rocks. It’s especially common as concretions in Dolostone and Limestone. Where these carbonate rock units are heavily weathered, large accumulations of Barite are sometimes found in the soil bedrock.

This mineral is commercially mined and rockhounds will visit these areas to collect the crystal specimens.

Barite can also be found as a concretion in sandstone. These concretions grow as Barite crystallizes within the interstitial spaces between grains of sand. Occasionally, Barite crystals grow into interesting shapes in the sand and are known as Barite Roses. These can be several inches long and incorporate large numbers of sand grains. Occasionally, Barite is so abundant in sandstone that it serves as the rock’s cement.

 

 

How to Identify Barite 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 Barite like a pro.

 

Visual Inspection

The visual inspection starts with what form of Barite 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? A cabochon should have a medium to high polish with little to no pitting. Barite cut en cabochon are beautiful pieces of artwork. The needle-like crystals within are present in many samples, but not all.

 

Is it faceted? If you have a faceted piece of Barite, it should be translucent. While Barite cabochons tend to have two or more colors, faceted varieties are typically a solid color. It’s common to find yellow, colorless, green, and grayish samples. You won’t find this mineral in jewelry but you could see it in a personal gem collection.

 

 

Is it a specimen? Barite 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 Barite displays when it’s a specimen.

• Barite typically forms tabular crystals but less often forms prismatic crystals or coarse, platy, or coxcomb-shaped aggregates.
• These specimens commonly form in divergent groups of tabular orthorhombic crystals called crested Barite or Barite Roses.
• It’s less common for Barite to form in stouter prismatic orthorhombic crystals.

 

Is it tumbled? It is not very common to find tumbled Barite because its hardness is below 5.

 

Physical Properties of Barite

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

 

Color: Colorless, White, Yellow, Brown, Blue, Gray – Colorless in transmitted light, also tinted Green, Blue, Brown, and Yellow

Clarity / Transparency: Transparent, Translucent, Opaque

Luster: Vitreous, Pearly

Cleavage: Perfect -Perfect on {001} Less so on {210} Imperfect on {010}

Fracture: Irregular/Uneven

 

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. Barite always produces a white streak.

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

 

Magnet Test

Barite is unusual because it is a diamagnetic mineral. Diamagnetism is a type of magnetism where certain minerals are repelled by externally applied magnetic fields and from internally induced magnetic fields in the opposite direction to that of the applied magnetic field.

 

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.  Barite has a hardness of 3 on the Mohs hardness scale.

 

Refractive Index Test

Determining the refractive index, or RI, as it’s referred to by gemologists for Barite, 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.

 

Barite’s Refractive Index: 1.636 – 1.648

 

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.

 

Birefringence Test

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: 0.012

 

Single or Double Refraction

Barite displays a very low 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.

Barite is transparent to translucent to opaque.

 

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.

 

Barite’s Specific Gravity: 4.50

 

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 Barite 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.