Thursday, July 21, 2016
Prasiolite: A Natural Gemstone? Or Heated Amethyst?
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.
Prasiolite is a great gemstone for gem collectors looking for distinct and attractive green color, availability in large carats, eye cleanliness and affordability.
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: