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 natural glass that is thought to have formed in the heat of an asteroid impact. This event occurred about 15 million years ago, and a splatter of hot glass formed a strewn field across central Europe.
Moldavite is usually yellowish green, green, or greenish brown in color. It has been cut into faceted and cabochon gemstones since the mid-1800s. These are used in rings, earrings, necklaces, pins and other types of jewelry.
Nice specimens of rough moldavite are popular with meteorite and mineral collectors. The extraterrestrial origin of moldavite gives it a special appeal to many people interested in new age, astrological, and spiritual practices.
Physical Properties of Moldavite
|Chemical Classification||A silica-rich glass|
|Color||Yellowish green, to 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. |
|Chemical Composition||Variable SiO2(+Al2O3)|
|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.|
Table of Contents
The Story of Moldavite Formation|
Moldavite as a Gemstone
Identifying Genuine Moldavite
Misnomers and Misspellings
The Story of Moldavite Formation
Moldavite is thought to have formed about 15 million years ago in the impact event that produced the Ries and Steinheim craters in southeastern Germany. An incoming asteroid is thought to have broken into two pieces that produced this pair of craters. The impacting bodies approached from the southwest. They 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 these materials "impactites." Moldavite is also considered to be a mineraloid because it is a naturally occurring, inorganic solid that does not have a crystalline structure. It solidified 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. It occurs as droplet-shaped particles of green to brown glass up to a few centimeters in diameter. Millions of pieces have been collected, mostly in the Czech Republic.  Specimens are often severely etched into unusual shapes by acidic subsurface waters.
Over the millions of years that have passed since the impact event which formed moldavite, much of the material has been eroded away, and much has been buried. As a result, moldavite is only found today in small areas of the original strewn field. These areas are shown on the accompanying map.
Moldavite as a Gemstone
Most gem-quality moldavite is faceted or cut en cabochon and sold as a collector's gem. Moldavite jewelry should be worn cautiously 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.
Nice pieces of rough moldavite are also 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.
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 faster 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 rough and gemstone moldavite being sold are undisclosed fakes. If you are purchasing moldavite online, there is a very good chance that you will receive imitation material. That's what we received when we purchased the green faceted "moldavite" shown in the image above. We paid $29.49 for the 13 millimeter x 11 millimeter, 6.19-carat stone. If it was a genuine moldavite, it should 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 selling dishonestly to make money. Be careful when buying moldavite. If you are offered a faceted moldavite over two carats or any moldavite without eye-visible bubbles, there is a good chance that it is fake.
Much of the moldavite being sold online today is offered for use as a “healing crystal” or for “metaphysical use.” Buyers believe that moldavite has beneficial properties, and that is the reason they seek it out. While some people say using moldavite this way is helpful, there is no scientific proof that moldavite has any medical effectiveness beyond that of being a placebo. But, when the seller fills this "prescription" with man-made glass, the buyer is definitely not getting his money's worth!
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 glass.
Most specimens of genuine moldavite contain trapped gas bubbles and flow structures that are visible under a magnification of 10x and often with the unaided eye. The gas bubbles are sometimes round, but more often they are elongate, stretched by the stress under which the glass cooled. The glass also contains flow structures of similar origin.
Most genuine moldavite has an unusually low refractive index. It typically ranges between 1.47 and 1.51, much lower than most minerals and many 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 mineraloid 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.
|Pictures of Opal|
|Ruby and Sapphire|
|Mined in America|
|Gem Mineral Collections|
Find Other Topics on Geology.com: