Even though obsidian and tourmaline are on opposite ends of the geological spectrum, they each have their unique qualities and interesting appeal. These two minerals show how many different things can be found in the Earth’s crust.

Obsidian comes from volcanoes. It has a smooth, glass-like look, and its colors are mostly dark and moody. On the other hand, Tourmaline has a prismatic, multi-faceted structure and a wide range of colors. It forms in various geological settings far below the surface of the Earth.

Even though obsidian and tourmaline seem very different, they have some surprising things in common that we’ll discover in this exploration. This will help us learn more about the fascinating world of mineralogy.

Obsidian vs. Tourmaline – The Major Differences

We’ll start by talking about what makes them different. They also have characteristics in common, but these are the most important differences to look for.

Appearance – Obsidian appears more like glass

Obsidian and tourmaline look different because their structures and textures are different. Obsidian is often called “nature’s glass” because it feels smooth and glassy. It has a smooth, polished surface that can be shiny and reflective.

This gives it a lustrous quality as a whole. When obsidian breaks, it does so in a way that is called a “conchoidal fracture pattern.” This means the pieces have smooth, curved surfaces with sharp edges, like broken glass.

Tourmaline has a crystalline structure with clear prism and column shapes. It doesn’t have a smooth surface like obsidian does. Instead, the crystal faces and edges give it a rough surface.

The transparency of tourmaline can range from clear to translucent. It has a unique look because it can get a vitreous (glass-like) or sub-vitreous luster when cut and polished.

The prismatic shape of tourmaline crystals and the fact that they can have two or three different colors in a single crystal give this mineral a unique look that makes it stand out from obsidian and a very popular gemstone.

Color – Tourmaline has a broader range of colors

Obsidian and tourmaline have very different colors, which makes them easy to tell apart in the mineral world. Obsidian is sometimes called “nature’s glass,” it usually comes in dark, solid colors, often jet black.

Obsidian doesn’t just come in black, though. It can also be brown, green, or even red. The different colors come from the other minerals mixed in with the rock.

For example, black obsidian has iron and magnesium, and green obsidian is green because it has different minerals.

On the other hand, Tourmaline has a wide range of colors that make it a true “chameleon” gemstone. This mineral comes in a wide range of colors, from bright pink (called rubellite) to lush green (called verdelite), mesmerizing blue (called indicolite), and even deep black (called charoite) (schorl).

The most exciting thing about tourmaline is that it can have two or three colors in a single crystal. This makes it possible to make gemstones with more than one color.

One of the things that makes tourmaline such a popular gemstone in jewelry and mineral collections is that it comes in many different colors and patterns.

Most obsidians and tourmalines are jet black, but other black rocks, gems, and minerals are equally fascinating.

Streak – Obsidian doesn’t have a streak

When it comes to streaks, obsidian, and tourmaline, exhibit significant differences. Obsidian, a type of volcanic glass, does not leave a line when scratched across a streak plate or porcelain tile.

Obsidian lacks the fine-grained, powdered form necessary for streak testing. Instead, it fractures conchoidally, producing smooth, curved surfaces with no distinct streak.

Tourmaline does have a streak, but it’s pretty even. Most of the time, the streak of tourmaline is white or has no color. This streak is made by scratching the mineral across a streak plate.

The color of the streak is determined by the powder left behind. Even though tourmaline’s streak color is usually hard to describe compared to its bright outside colors, it can still be used to identify tourmaline when combined with other physical and optical properties.

So, in streak tests, obsidian is hard to determine because it doesn’t leave a streak. But, tourmaline leaves a faint, colorless streak.

Hardness – Tourmaline is harder

When it comes to hardness, which is how resistant a mineral is to being scratched, obsidian and tourmaline are very different. Obsidian is about 5.5 on the Mohs scale, which is not as hard as many other minerals.

This means harder things like steel, quartz, or even a simple knife blade can easily scratch obsidian. It isn’t very hard because it has an abstract, glass-like structure and doesn’t have the strong atomic bonds that crystalline minerals do.

The Mohs scale says that tourmaline is much harder than obsidian. Its hardness is usually between 7 and 7.5. This puts tourmaline in the group of minerals that are between soft and hard.

It can stand up to rubbing and scratching from most materials, even obsidian. The crystalline structure and strong atomic bonds inside the crystal lattice of tourmaline make it hard.

Tourmaline is more durable and strong than other materials because it’s harder. This is one reason it is so famous for making gemstones and jewelry, where durability is important.

Crystal Structure – Obsidian has no crystal structure

The crystal structures of obsidian and tourmaline are very different. Obsidian, which is often called “volcanic glass,” has no crystal structure at all. Instead, it is amorphous, which means that its atoms are not arranged in a way that repeats itself like they are in crystalline minerals.

Obsidian is made when molten lava cools quickly, so its structure resembles natural glass. Because it doesn’t have a crystal lattice, it looks smooth and glassy and breaks into conchoidal pieces when it breaks.

Tourmaline has a crystal structure that is clear and easy to see. It forms long, prismatic crystals with a triangular cross-section, crystallizing in the trigonal system.

The size and shape of these crystals can be different, but they all have the same basic structure. Tourmaline’s unique physical properties, like how hard it is and how it conducts electricity, come from how its atoms are arranged.

Because of its crystalline structure, tourmaline can have a wide range of colors and even two- or three-color patterns within a single crystal. This makes it a very popular gemstone and a collector’s item.

Chemical Composition – Tourmaline has a complex boron silicate mineral

The chemicals that make up obsidian and tourmaline are very different. Obsidian is mostly made up of the chemical compound silica (SiO2), also found in quartz.

But, unlike quartz, obsidian doesn’t have a clear structure of crystals. Along with silica, obsidian can have varying amounts of other elements and minerals, such as iron, magnesium, and feldspar, which contribute to its color and impurities.

Depending on where the obsidian comes from, it can have a different mix of minerals.

On the other hand, Tourmaline is made up of many different chemicals. Its general formula is (Na,Ca)(Fe,Mg,Li,Al)3Al6(BO3)3Si6O18(OH), which shows that it contains sodium (Na), calcium (Ca), iron (Fe), magnesium (Mg), lithium (Li), aluminum (Al), boron (B), silicon (Si), and oxygen (O).

Tourmaline can be a wide range of colors because of this complex mix of elements. Different trace elements and impurities can replace some of its main components, changing the color.

Tourmaline is known for its complex chemical makeup, which is part of what makes it a unique and desirable gemstone.

Density – Obsidian has a lesser density

When it comes to density, which is how much mass a substance has per unit volume, obsidian and tourmaline are very different. Obsidian is usually between 2.35 and 2.65 grams per cubic centimeter (g/cm3) dense.

Compared to other minerals, this means it has a density that is somewhere between low and moderate. Obsidian’s density can change depending on its make-up and whether or not it has impurities, both of which can affect its specific gravity.

Tourmaline tends to be more dense than obsidian. Most of the time, its density is between 2.9 and 3.3 g/cm3. This is because tourmaline comprises many different elements, like sodium, calcium, iron, and boron, and has a complex chemical makeup and crystalline structure.

Even though the range of densities for tourmaline and obsidian may overlap, tourmaline usually has more mass per unit volume, making it a denser mineral overall.

Formation – Obsidian forms in volcanic environment

Obsidian and tourmaline have strikingly different formation processes. Obsidian is the result of volcanic activity. It forms when molten lava from a volcano cools rapidly upon contact with the air or water.

This rapid cooling prevents the minerals in the lava from crystallizing, forming amorphous, glassy obsidian. The exact composition and appearance of obsidian can vary depending on the original lava’s chemical makeup and the cooling speed.

Like the western United States and Iceland, volcanic regions with past or present volcanic activity are common obsidian sources.

Tourmaline forms deep within the Earth’s crust under various geological conditions. It can develop in various settings, including granite pegmatites, metamorphic rocks, and hydrothermal veins.

The precise conditions under which tourmaline crystallizes lead to its remarkable diversity in colors and crystal structures. For example, pink tourmaline (rubellite) often forms in granitic pegmatites, while black tourmaline (schorl) can be found in schist and other metamorphic rocks.

The multiple formation environments contribute to the wide distribution of tourmaline deposits worldwide, from Brazil and Sri Lanka to Afghanistan and the United States.

Fluorescence – Tourmaline exhibits fluorescence

Obsidian and tourmaline differ notably in their fluorescence properties when exposed to ultraviolet (UV) light. Most of the time, obsidian doesn’t glow under UV light.

This means that when UV light is shone on obsidian, it doesn’t give off visible light in response. Instead, it stays dark and doesn’t react to the UV source. One thing that makes obsidian different from other minerals that might fluoresce under UV light is that it doesn’t.

When tourmaline is exposed to UV light, it can fluoresce. Tourmaline can glow in different ways depending on its chemical makeup and impurities. When exposed to UV light, some tourmaline pieces may fluoresce in different colors, such as pink, green, or blue.

This property of fluorescence can be used to help identify gemstones. It can add to the beauty of tourmaline specimens, making them even more sought after by collectors and gem lovers.

So, obsidian doesn’t change when exposed to UV light, but tourmaline’s fluorescence can be a fascinating quality that adds to its overall appeal.

Conductivity – Obsidian can’t conduct electricity

Obsidian and tourmaline exhibit significant differences in terms of their electrical conductivity. Obsidian is a poor conductor of electricity, meaning it does not allow the flow of electrical current through it.

This is because obsidian primarily comprises amorphous silica (SiO2), which lacks the free ions or mobile electrons necessary for electrical conductivity.

As a result, obsidian does not display any notable electrical properties and is not used in electrical or electronic applications.

There are some interesting electrical properties that tourmaline can have. Even though it doesn’t conduct electricity very well, some types of tourmaline can show weak electrical conductivity in certain situations.

This property is called “piezoelectricity,” meaning that tourmaline makes an electric charge when a force is put on it. Tourmaline can also have pyroelectricity, which means that when the temperature changes, it gives off an electric charge.

Because of these unique electrical properties, certain types of tourmaline are helpful in specific applications like pressure sensors and devices sensitive to temperature.

Location – Tourmaline is found in a wide range of locations

Obsidian and tourmaline are found in different places because of how they formed and where they came from on the earth. Obsidian is often found in areas where volcanoes have erupted in the past.

Some of these places are in the western United States, especially in California, Oregon, and Nevada, where large amounts of obsidian have been formed by volcanic activity.

Iceland, South America, and the Mediterranean also have obsidian deposits. Volcanic activity in the past was a key factor in how obsidian formed.

Check out our guide on how to find crystals near you to increase your chances of finding tourmaline or obsidian.

Tourmaline can be found in many different types of geological settings worldwide. It can be found in metamorphic rocks, hydrothermal veins, and granite pegmatites, mineral-rich igneous rocks with large grains.

Brazil, Sri Lanka, Afghanistan, and the United States are good places to find a tourmaline. For example, the Pala district of California is known for its pink and green tourmaline, and the Paraba district of Brazil is known for its beautiful tourmaline.

Each place has different kinds and colors of tourmaline from the different geological environments where they formed. Because tourmaline is found worldwide, it’s a popular and highly valued gem in the jewelry and gem-collecting worlds.

The places where we can find these rocks can tell us about their geological history. Even though rockhounding is a general hobby, you can find obsidian and tourmaline in these best rockhounding locations.

Price – Obsidian is more affordable

Obsidian and tourmaline have very different market prices, primarily because of how rare they are, how much people want them, and what they are used for. Most of the time, obsidian is cheaper than tourmaline.

Obsidian is cheap because it can be found in many places and easily get out of the ground. It’s often used to make decorations, arrowheads, and inexpensive jewelry.

Obsidian pieces have different prices depending on their size, quality, and how well they were made, but overall, collectors and regular people can buy them reasonably.

Tourmaline is known for having a wide range of prices, with some types being very expensive. Tourmaline’s price depends on many things, such as its color, clarity, size, and where it comes from.

Rare and highly sought-after types of tourmaline, like Paraba tourmaline, can be among the most expensive gems in the world, with prices that often match or even beat those of diamonds.

Because tourmaline comes in so many colors and is so popular on the gemstone market, it has a wide range of prices. Anyone can buy some pieces, while others are only wanted by serious gem collectors and high-end jewelry designers.

Check out our guide for more specific pricing information about obsidian’s value and tourmaline’s price.

Tourmaline vs. Obsidian – The Similarities

After talking about how different tourmaline and obsidian are, we’ll discuss how they’re the same. Although they have fewer similar characteristics than differences, it’s still vital to know this information about these minerals.

Luster – Tourmaline and Obsidian both have a glassy luster

In mineralogy, the word “luster” is used to describe how light interacts with the surface of a mineral to make it look a certain way. Both obsidian and tourmaline have a shine that is similar in some ways.

Obsidian has a glassy luster, meaning its surface looks smooth, shiny, and reflective, like glass. Obsidian’s amorphous, non-crystalline structure lets light pass through and reflect off its surface, giving it a polished and glossy look.

In the same way, tourmaline can have a glass-like shine. Even though tourmaline is more crystalline than obsidian, its surface can also look smooth, shiny, and reflective when polished.

This glassy sheen gives tourmaline gemstones and specimens an eye-catching look that adds to their beauty.

Even though this vitreous luster can be found in both obsidian and tourmaline, it’s important to remember that tourmaline’s luster can change depending on its type and color.

Some kinds of tourmaline can have a sub-vitreous luster, which is less glassy than a vitreous luster but is still shiny and attractive.

Cleavage – Tourmaline and Obsidian have little to no cleavage

Cleavage is an important property that describes how a mineral breaks along certain planes of weakness. This is because of how the atoms are arranged in the crystal lattice.

Obsidian and tourmaline are similar in that they don’t usually have clearly defined cracks. Obsidian, made of volcanic glass, has no cracks at all. Instead, it does so in a unique conchoidal pattern that makes smooth, curved surfaces when it breaks.

This crack is smooth, and there are no transparent planes of weakness. Obsidian is amorphous, meaning its atoms are not arranged in a repeating, crystalline lattice. This means that it doesn’t break apart when it’s broken.

Even though tourmaline has a crystalline structure, it usually has poor to unclear cleavage. Tourmaline’s cleavage is usually not well-developed or easy to see, breaking in odd ways.

Some minerals have transparent cleavage planes that break cleanly, but tourmaline’s cleavage isn’t usually a big deal. Instead, it tends to break unevenly and conchoidally, like obsidian, because of how its atoms are arranged and its crystals are built.

Magnetism – Neither Obsidian nor Tourmaline are magnetic

Magnetism is a property that has to do with how a substance reacts to magnetic fields. Obsidian and tourmaline usually don’t have any very strong magnetic properties.

Obsidian is a type of glass from volcanoes, so it is usually not magnetic. It’s not affected by magnets because it is not solid and has no magnetic parts.

Obsidian is not magnetic because when a magnet is brought close to it, there is usually no noticeable attraction or repulsion.

Most common types of tourmaline do not have strong magnetic properties either. Even though tourmaline can have small amounts of iron in its chemical makeup, the amount of magnetic elements in it is usually not enough to make it strongly magnetic.

Some rare types of tourmaline, especially those with a lot of iron, may have weak magnetic responses, but this is not something that most people think of when they think of tourmaline.

Obsidian and tourmaline are usually not magnetic or are only very weakly magnetic. These minerals don’t attract magnets like iron or magnetite do. Collectors, geologists, and researchers all need to know that obsidian and tourmaline are not magnetic to identify and work with them.

The Easiest Ways To Tell Obsidian and Tourmaline Apart

If you look at more than one thing, it can be easy to tell the difference between obsidian and tourmaline. Trying to figure out how to tell them apart is an exciting game. Even though they have some things in common, there are a few key differences you should look out for.

Their looks are the most important clue

The color is one of the things that stands out the most. Obsidian is usually black, but it can also be brown, green, or red if there are impurities or other things.

On the other hand, tourmaline can have a wide range of colors, from pink and green to blue, black, and more. Some tourmaline pieces have two or three different colors in a single crystal.

Tourmaline is more likely to be the mineral you’re looking at if it has a lot of different colors.

Check their light transmission

Transparency is another important difference. Obsidian is usually opaque, which means it doesn’t let light through and you can’t see what’s behind it.

Conversely, Tourmaline can be clear, see-through, or even opaque, letting some light through. Depending on the type and variety of tourmaline, the amount of transparency can be different.

Test their hardness

Even though obsidian and tourmaline are pretty hard minerals, they do not have the same hardness level. Obsidian is about 5.5 on the Mohs scale of hardness, which means it is not very hard.

On the Mohs scale, tourmaline usually scores between 7 and 7.5. If you can use common materials (like a glass plate) to test the mineral’s hardness, this can be a valuable way to tell them apart.