A green gem formed by an ancient asteroid impact
Author: Hobart M. King, Ph.D., GIA Graduate Gemologist
What is Moldavite?
Moldavite (also called Bouteille Stone or vltavin) is a yellowish green to greenish brown brown natural glass that is thought to have formed during an asteroid impact about 15 million years ago in central Europe. The green glass can have an attractive color and has been cut into gemstones since the mid-1800s. These are used as a novelty gem in rings, earrings, necklaces, pins and other types of jewelry. Specimens of moldavite are also popular with meteorite and mineral collectors.
Physical Properties of Moldavite
|Chemical Classification||A silica-rich glass|
|Color||Green to greenish brown|
|Diaphaneity||Transparent, translucent, opaque|
|Mohs Hardness||5 to 5.5|
|Specific Gravity||2.32 to 2.40|
|Diagnostic Properties||Green to brown color. Under magnification: lechatelierite (a high-temperature form of SiO2) inclusions, abundant gas inclusions, and flow lines. |
|Uses||A novelty gemstone. Specimens for meteorite and mineral collections. Many people believe that moldavite has certain healing properties and pay a premium price for it. There is no scientific evidence that moldavite has any medical effectiveness beyond being a placebo.|
The Story of Moldavite Formation
Moldavite is thought to have formed by the impact event that produced the Ries and Steinheim craters in southeastern Germany. The impacting bodies hit with a high enough velocity to melt and splatter the target rock across a strewn field that includes portions of what is now the Czech Republic, Austria, and Germany.
Most of the splatter solidified in the air and fell to Earth in the Czech Republic.  Meteorite experts have named such materials "impactites." Moldavite is also considered to be a mineraloid because it is a naturally occurring, inorganic solid that does not exhibit crystallinity. It crystallized so quickly that atoms did not have enough time to organize themselves into minerals.
Today moldavite is found in sediments of Middle to Upper Miocene age as droplet-shaped particles of green to brown glass a few centimeters in diameter or smaller. Millions of pieces have been collected, mostly in the Czech Republic.  Specimens are often severely etched into unusual shapes by acidic subsurface waters.
Moldavite as a Gemstone
Nice pieces of rough moldavite are often used in jewelry. Attractive droplet-shaped pieces are commonly wire-wrapped and made into pendants or earrings. Rough moldavite specimens with representative features are also purchased by meteorite and mineral collectors. The best specimens are often purchased by collectors for a much higher price than what they would have sold for if they were used in jewelry.
Most gem-quality moldavite is faceted or cut en cabochon and sold as a novelty gem. Moldavite must be used with great care in jewelry because it is brittle and has about the same hardness as most man-made glasses (5 to 5.5). For that reason it is best used in earrings, pins and pendants that will not be subjected to impacts or abrasion. Moldavite has a durability that is too low to be a good gem for rings. When it is used in a ring, a metal bezel or other feature should protect the gem from impact and abrasion.
Faceted moldavite and cabochons have been placed in jewelry since the late 1800s. Once moldavite’s extraterrestrial origin was known, the demand for moldavite gems grew much higher than the natural material could be found.
To meet the demand, enterprising people began faceting "moldavite" from green bottle glass. Then glassmakers in China began manufacturing glass in just the right green color to be deceptively sold as “moldavite.” Fake moldavite began streaming into the market. Fake moldavite even made its way into museum collections. 
Today, much of the moldavite specimens being sold are undisclosed fakes. If you are purchasing moldavite online, there is a good chance that you will receive imitation material. That's what we received when we purchased the green faceted "moldavite" shown at the top of this page. We paid $29.49 for the 13 millimeter x 11 millimeter, 6.19 carat stone. If it was a genuine moldavite, it would have cost a lot more. It is an enormous stone for moldavite - most faceted stones cut from genuine moldavite are much smaller.
The difference between “imitation” and “fake” is in the disclosure. “Imitations” are sold as such. “Fakes” are sold without disclosure. The seller might not realize that the material is “fake,” or the seller might know and is simply selling to make money.
Much of the moldavite being sold online today is offered for use as a “healing crystal” or for “metaphysical use.” While some people might find benefits in using moldavite these ways, there is no scientific proof that moldavite has any medical effectiveness beyond that of being a placebo - and much of the moldavite being sold for these uses isn't even the real thing!
Identifying Genuine Moldavite
Unlike most gem materials that grow slowly over time in a quiet underground environment, moldavite formed in a burst of heat and energy produced by one of the most violent possible events - the impact of a large hypervelocity object with a planet. The rock in the impact area was instantly vaporized by the heat of the impact, then immediately condensed into a molten liquid, and then almost immediately solidified into an amorphous glass. The condensation and solidification were so fast that mineral crystals did not form, and gases were trapped in the moldavite glass.
Most specimens of genuine moldavite contain trapped gas bubbles and flow structures that are visible under magnification. The gas bubbles are sometimes round, but more often they are elongate shapes, stretched by the stress under which the glass cooled. The glass also contains flow structures of similar origin.
Most moldavite has an unusually low refractive index. It typically ranges between 1.47 and 1.51, much lower than most minerals and most man-made glasses.
The most diagnostic feature seen under magnification in some moldavite specimens is high relief, wire-shaped inclusions of lechatelierite, a high-temperature form of SiO2. Unlike quartz, lechatelierite is not a mineral; it is a mineraoid formed by instantaneous events, such as asteroid impacts, atomic blasts, and lightning strikes. 
An excellent article for information about how to identify genuine moldavite is "Moldavites: Natural or Fake?" authored by Jaroslav Hyrsl and published in the Spring 2015 issue of Gems and Gemology. 
 Numerical Modeling of Tektite Origin in Oblique Impacts: Natalia Artemieva, Elisabetta Pierazzo, and Dieter Stoffler, Bulletin of the Czech Geological Survey, Volume 77, Number 4, pages 303-311, 2002.
 Moldavites: A Review: Milan Trnka and Stanislav Houzar, Bulletin of the Czech Geological Survey, Volume 77, Number 4, pages 283-302, 2002.
 Moldavites: Natural or Fake? Jaroslav Hyrsl, Gems & Gemology, Volume 51, Number 1, 2015.
 Lechatelierite Mineral Data: a Webmineral.com article accessed in July, 2017.
Misnomers and Misspellings
Moldavite is referred to by a number of incorrect names. These include: glass meteorite, bohemian chrysolite, false chrysolite, glass chrysolite. These names are misnomers because moldavite is not a meteorite or a chrysolite (a name used for a yellowish-green variety of the mineral olivine, which when of good clarity and color is known by the gemological name of peridot).
Moldavite is without question one of the most frequently misspelled gem materials. Common misspellings include: moldivite, moldovite, moldevite, moldervite, moltavite, modavite, and muldavite. Fortunately, for the people who misspell, Google has learned that most people who use these misspellings as search queries are actually looking for information about “moldavite” and returns useful results.
|Ruby and Sapphire|
|Pictures of Opal|
|United States Gemstones|
More From Geology.com: