Black Tourmaline? Obsidian? How to Tell the Difference

Translucent (see the shadow?) Black Obsidian (L), Black Tourmaline Nugget (R)

Black Tourmaline and Black Obsidian are two of several gemstones that are shiny and black, and they can appear somewhat similar. So how can you tell the difference? I recently had an encounter with a customer who felt that the black tourmaline necklace she purchased was obsidian and not tourmaline (although it was definitely tourmaline!).  Well, in case other people are also confused regarding the difference between Black Tourmaline (a mineral) and Black Obsidian ("mineraloid" natural volcanic glass), here is some information I hope you find helpful!

BLACK TOURMALINE
Tourmaline is a beautiful gemstone that comes in many colors, and since it can't be created in a lab (so only natural Tourmaline is found), it can be very expensive.  Black Tourmaline, or "Schorl", is an inexpensive type of genuine Tourmaline---it's a rich black opaque color, and is found in abundance all over the world.  Sometimes in bright light you can see glints of red--that's due to iron in the gem. It grows within host rock, in large crystals, small crystals, and in various nugget and chunk forms.  Rough tourmaline can be left to look rough, or it can be polished, sliced, or faceted.  If you are looking for Tourmaline to wear for its metaphysical properties, Black Tourmaline is a great and affordable choice.

Here are some examples of Black Tourmaline----if you google that, you can see a very wide variety of  sizes and shapes of tourmaline nuggets, crystals, shards, etc.  Here are pictures of rough chunks of Black tourmaline, taken from various geologic and gemstone websites:

That last picture is from an Etsy seller---a very reputable, large-volume gemstone seller, who correctly describes these as "Tourmaline Gemstone Top-Drilled Large Raw Shards. Semi-Precious Gemstones."

And here is the actual strand of these types of "shards" of rough black Tourmaline that I purchased from another lovely seller on Etsy:

And it was one of those shards in that strand (right in the front!) that I sold to the one Amazon buyer who claims it's "obsidian".  As you can see, these shards look the SAME as the rough pictured above---especially in pictures 3 and 4!  These shards have been sliced and polished on the back, and the rough "lumpy" part is on the front.

Here is my favorite picture of tourmaline "in the rough".  It's a picture taken from the GIA website (Gemological Institute of America) in an article discussing Emeralds...but here is a large growth of Black Tormaline, plus Emerald, Mica, Pyrite and Quartz.  But look at the "lumpy" as well as "crystal" nature of this large Tourmaline find:

I love how this shows the wide variety of shapes and forms of Black Tourmaline.  It also shows the distinctive "lumpy" rough texture that the tourmaline shards that I purchased exhibit.  The upper right looks almost like burnt bark---and sort of like black lava rock! I would LOVE to have a piece of that beautiful emerald!!!

There are "crystals" of black Tourmaline as well.  These are found and sold in large nuggets, with more of a hexagonal crystal structure visible, and sometimes with crystal "tubes" than run along the length of the nugget. Often they look a lot like pieces of black licorice.  Some are very shiny and black.  Often they have very visible fractures and other surface cracks and flaws.  Here are some examples:

So you can see a wide variety of Black Tourmaline shapes---from crystals to nuggets to lumps and shards.


OBSIDIAN
Black Obsidian is black volcanic glass.  It is translucent--not completely opaque.  It's considered to be a mineraloid gemstone despite the fact that there is no mineral crystal structure in glass.  But it is natural, very shiny and black (and can also be smokey grey, brown, rusty red, banded, with "snowflakes" and in other colors).  Obsidian has a smooth uniform texture, and breaks with "conchoidal fractures" or semi-circular patterns.  This is distinctive to obsidian and glass:

Now, both black tourmaline and obsidian are black and shiny.  But obsidian does NOT have the rough and lumpy texture that tourmaline has.  Plus, when obsidian is carved or split or broken, it fractures in distinctive round radiating circles---like when  you toss a rock into a lake.

Incidentally, the value for black tourmaline and black obsidian is about the same, although there are many instances where obsidian is far more valuable than black tourmaline.  Obsidian is often used in making black opal doublets and triplets.

Obsidian, being glass, is VERY sharp when broken, so there is no such thing as "shards" of obsidian that are drilled and sold as pendants.  (Haha---reminds me of the old SNL skit about a terrible kids' toy called "Bag O' Glass"!)   There are polished obsidian beads.  Most obsidian is sold in chunks for gem collectors.

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So really, it's pretty easy to tell Black Tourmaline from Black Obsidian, just from the pictures!  And having it examined by a gemologist would tell you FOR SURE if it's glass or a mineral.  

Other gems that look very similar to these black gems are Black Onyx and Hematite, and even Black Spinel.  Chalcedony quartz is sometimes dyed black to look like Black Onyx.

Tourmaline is a beautiful gemstone and comes in many colors, including multi-hued gems such as Watermelon Tourmaline.   Here are some incredibly beautiful shards of genuine tourmaline, and the price for these on Etsy (they are about dime-sized) is just under $1,000:

Don't they look like stained glass shards?  They're so beautiful!  And definitely NOT glass!!

Prasiolite: A Natural Gemstone? Or Heated Amethyst?

A few months ago, someone sent me an email regarding a Prasiolite necklace I had in my shop.  It was brief: "Is this natural Prasiolite, or heated Amethyst?"  And before I could answer, she wrote back: "Never mind. I read your description."  And then I never heard from her again.

A classic case of the old Asimov question----did she want the answer that's true, or the one that satisfies?  Most people don't want the truth, which is strange!

I would have told her that there is NO "natural" Prasiolite available in the marketplace.  But she didn't want to hear that---she wanted to believe some sellers who claim to offer "natural, untreated Brazilian Prasiolite."  And that is definitely NOT the truth!

What Is Prasiolite?
Prasiolite is the name of the gemstone that is transparent celadon-green quartz.  Amethyst is transparent purple quartz.  Citrine is transparent yellow quartz.

Is it the same as Green Amethyst?
Yes.  Prasiolite is often referred to as "Green Amethyst".  It's also called Vermarine, Lime Citrine, and just Green Quartz.

Is it Natural?
Although there has been a VERY small amount of natural Prasiolite found in nature, ALL of the prasiolite that you see commercially is treated Amethyst, or perhaps treated Citrine.  In fact, I read that the Smithsonian Institution has a very small piece of a fractured crystal of Prasiolite green quartz dated from 1884. But I couldn't find a picture of it, or any information about it, on the Smithsonian website.  And a rare gems specialist, K and K International of Virginia, has some small .40-ct. faceted natural green Prasiolite gems which they've had in their collection for years.  So virtually all the Prasiolite you can find in jewelry is treated Amethyst (or Citrine) from Brazil.

It's interesting to note that there is NO WAY to determine if a Prasiolite specimen is naturally heated or heat-treated.

Also, the color can fade over time, and with exposure to sunlight.

How is it Treated?
Prasiolite occurs when amethyst or citrine undergoes a heat treatment while in the presence of iron, transforming the quartz into a beautiful pale celadon green. This heating mimics how nature produces this gem.  Even though quartz is, by nature, relatively inclusion-free, exceptionally clean crystal rough is selected for this heating process. This clean rough assures even color distribution.   Most prasiolite comes from the Montezuma mines at Minas Gerais, Brazil.   Colors can range from the very palest of green to a deeper more intense celery green.

Only 30% of quartz undergoing this treatment transforms into the cool green color. Without proper identification, some of it might be mistaken for green beryl or a light-toned green tourmaline!

Recently, some Prasiolite has been formed by heating Smoky quartz.  The result is a darker, dusky green color.

Unusual Cuts

Prasiolite is often cut into large carats with complex, intricate or unusual cuts to bring out the color of the stone.  Concave cuts, checkerboard cuts, triangular cuts,  and microfaceted briolettes are often seen.

Why Prasiolite?
Prasiolite is a great gemstone for gem collectors looking for distinct and attractive green color, availability in large carats, eye cleanliness and affordability.





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I would like to just reiterate that ALL of the prasiolite found in the marketplace is heat-treated amethyst or citrine.  There is VERY LITTLE of the natural green quartz, and that would be found in very old jewelry or in old mineral collections.

Also, I want to add that sellers who offer "created" quartz----maybe called "not natural", or "lab grown" or "hydro quartz"---they're really offering colored glass.  FYI, just a few years ago, so-called "Hydro Quartz" was sold as "hydro quartz glass" usually from China or India.  Somehow, the word "glass" has dropped off and people are claiming this glass to be a gemstone.  I've written other posts about this, including pictures of huge slabs of this colored glass rough for sale in China and Thailand.  And it's clearly being sold as "fused glass" or "hydro quartz glass". HERE is a website that sells this glass.  And HERE they're offering "fused silica--jeweler's silica" which is glass being sold specifically as gem simulants.

Again, I've taken MANY samples of hydro quartz----now over 50 different samples----to be examined by a gemologist, who looks for crystal structures within the stone.  If there is no crystal structure, it's glass.  There are other tests as well.  And NONE of the samples I've ever seen were anything other than glass.

Quartz is the second most abundant mineral on earth (second to feldspar).  It naturally grows in HUGE clear and beautiful crystals---amethyst (purple quartz) is the most expensive quartz.  SOMETIMES labs will grow Amethyst in a lab, which results in a very dark amethyst with bright red flash ("Siberian" is the color).  That is because that deep Siberian purple/red color is cost-effective to grow and then sell.  Also, dying clear quartz purple will result in a quickly-fading color (and so purple "doublets" can be found---utilizing a purple bonding agent between two clear quartz slices). Clear quartz is grown in labs, but mostly for the electronics industry and other commercial industries.  Hydrothermal process gems are definitely grown---expensive synthetic gems such as corundum (sapphires and rubies) and emeralds.  Synthetic gemstones are lab-grown but possess the same physical, chemical and optical properties as their natural counterpart.  So a synthetic sapphire IS a sapphire.   Tourmaline, FYI, is still not successfully lab-grown so only natural tourmaline is available.

So when you see such things as "ruby quartz" or "paraiba quartz" or "tanzanite quartz" or "emerald quartz" or "rubellite quartz" --- stones with vibrant colors and names of actual gemstones to describe the product---those are hydro quartz, which were always known as hydro quartz glass.  I have seen "prasiolite hydro quartz" for sale and now THAT can't even be possible! 

Reputable gemstone wholesalers, who sell gems to jewelers (such as Rio Grande Jewelry) do not sell "hydro quartz" at all.  They only deal with actual gemstones.

If you can't find something listed on the GIA.edu website, or the ICGA (gemstone.org) then you should question the validity of a "gemstone" offered.  Or send them an email---a certified gemologist will get back to you and would be glad to answer your question!

I was looking at Prasiolite (green amethyst) on Etsy today and I saw this pair of earrings being sold as "green amethyst" and they are over $200!!  Take a look:

Now, I don't know about you, but on MY monitor, those are blue.  They're like the color of Windex.  And the color isn't really saturated and....well, as you can see, these are NOT prasiolite, and I'm very sure they are glass.   Perhaps some wholesale seller told her they are "natural"! But there's NO EXCUSE for something like this, something this fraudulent.  Any jewelry seller needs to take responsibility and find out what they're offering!  The description further states that these "Green Amethyst" earrings are "UNTREATED"!!!  Well even if they were actual Prasiolite, they would absolutely BE treated---that's how prasioliate is made!!  Heat treating purple quartz!!!   Those are obviously glass and they look more like those Swarovski "column" crystals than they do any quartz.