Short answer: both are natural glasses made by meteorite impacts, but from different events 14 million years apart. Moldavite is bottle green to olive glass from the Ries impact in southern Germany about 15 million years ago, found mostly in the Czech Republic. Libyan desert glass is pale yellow, almost pure silica (about 98%) from the Egyptian Sahara, about 29 million years old, with no crater yet found. Color, surface texture and weight per size separate them in the hand.
How do the numbers compare?
Fourteen million years, a few hundred kilometers of strewn field versus a patch of desert corridors, and a chemistry gap of about twenty percentage points of silica: the table puts the two side by side.
| Moldavite | Libyan desert glass | |
|---|---|---|
| Color | Bottle green, olive, greenish brown | Pale yellow to yellow green, often milky |
| Age | About 15 million years | About 29 million years |
| Source event | Ries impact, southern Germany | Impact in the Egyptian Sahara, crater unknown |
| Silica content | Tektites run 68 to 80% | About 98% |
| Specific gravity (IGS table) | 2.27 to 3.40 | 2.21 |
| Refractive index | 1.48 to 1.54 | 1.462 |
| Hardness | 5 to 5.5 | Harder than knife steel, softer than quartz |
| Largest known piece (IGS table) | 235 g | 4,500 g |
| Typical surface | Deeply etched, sculpted, pitted | Wind-polished, frosted or faceted by sand |
| Found in | Czech Republic, also Germany and Austria | Great Sand Sea, near the Egypt and Libya border |
The specific gravity, refractive index and largest-size figures are from the International Gem Society's tektite table (IGS tektite). The silica figures are from a 1979 Aramco World review by John W. Olsen and James R. Underwood, which put tektites at 68 to 80 percent silica and Libyan desert glass at approximately 98 percent (Aramco World). The age of Libyan desert glass comes from Curtin University researcher Aaron Cavosie writing in The Conversation (The Conversation).
How did each glass form?
Moldavite: splash from a crater that still exists
Geology.com describes moldavite as natural glass formed in the heat of an asteroid impact about 15 million years ago, with a splatter of hot glass forming a strewn field across central Europe (Geology.com). The impactor came from the southwest; the Ries and Steinheim craters mark the impact sites and the melt was thrown northeast. The IGS adds that moldavites formed at distances up to 280 miles from the crater, and that, by definition, only glass from the Nördlinger Ries impact can be called moldavite (IGS moldavite). The moldavite guide covers the crater and the strewn field in more depth.
Libyan desert glass: melted sand, crater missing
Libyan desert glass took longer to explain. It is nearly pure silica, and Cavosie notes that melting it requires temperatures above 1,600°C, hotter than any igneous rock on Earth. Two ideas competed for decades: a ground impact, or a giant airburst that melted the surface without leaving a crater. The evidence that settled it sits in grains of zircon smaller than the width of a human hair. About 10% of them preserve the fingerprint of reidite, a high-pressure mineral that forms only in meteorite impacts. The team found that fingerprint in every one of seven samples examined, and published the result in the journal Geology in 2019. Archaeology magazine quoted Cavosie calling it "the first bulletproof evidence" for an impact (Archaeology). The crater itself has still not been located; it may be buried under dunes or eroded away.
The glass also carries rare high-temperature minerals: cristobalite, a form of silica, and zirconia that grew when most of the zircon broke down above 1,700°C. Those are lab-scale features, though, not something a loupe will show.
Is Libyan desert glass a tektite?
It depends on who is classifying. The IGS includes it in its tektite table alongside moldavite, australite and indochinite. The Aramco World authors were more cautious: Libyan desert glass has uniformly higher silica than tektites, shows no aerodynamic sculpturing, and many fragments are tabular and layered, a shape seen in only one kind of tektite. The practical label used by most geologists now is impact glass, and the planned impact glass guide explains the difference: tektites are melt thrown far through the air, while some impact glasses formed close to the impact site.
How can you tell them apart in hand?
Color
The easiest check. Moldavite is green, ranging from olive and yellowish green to bottle green, a color the IGS attributes to a low concentration of iron. Libyan desert glass is pale yellow to faintly greenish yellow and often slightly cloudy. A yellow "moldavite" or a deep green "Libyan desert glass" is mislabeled.
Surface
Rough moldavite has a sculpted, deeply etched skin. Geology.com explains that specimens are often severely etched into unusual shapes by acidic subsurface waters. Libyan desert glass lay on the open desert surface instead, and the Aramco World review describes many exposed fragments as highly polished and faceted by wind and sand. Expect frosted, smooth, sandblasted faces rather than ridges and spikes.
Weight for size
Libyan desert glass is the lighter of the two. Aramco World notes that fragments are somewhat lighter than tektites of equal size, which matches the IGS figures (2.21 against moldavite's higher range). A careful hydrostatic weighing separates them; a hand comparison of two same-sized pieces often does too.
Size of the piece
Large moldavite is rare: the IGS table gives 235 g as the largest known. Libyan desert glass comes much bigger, up to 4,500 g in the same table, and the Aramco authors describe pieces the size of a person's head weighing over 16 pounds. A fist-sized "moldavite" at a modest price should raise questions; a fist-sized Libyan desert glass is believable.
Inclusions
Both can contain bubbles. Moldavite's diagnostic inclusion is lechatelierite, wire-like silica glass that the IGS calls a strong indication of moldavite. Our fake moldavite guide walks through that check. Libyan desert glass is better known for dark streaks and wisps, and it does not show moldavite's swirled green flow texture.
Which one has the longer human history?
Libyan desert glass, by a wide margin. The Aramco World review records that a Desert Survey expedition led by P. A. Clayton found pale yellow-green glass on December 29, 1932, in an area of roughly 80 miles by 30 miles between the dunes of the Sand Sea. People had found it long before that. Stone Age Aterian toolmakers flaked it into implements, and Clayton and L. J. Spencer reported that at least 10 percent of the flakes they recovered showed signs of human workmanship. The most famous carved piece is the yellow-green scarab at the center of a pectoral from the tomb of Tutankhamun, which the IGS notes was identified as Libyan desert glass in 1996 at the Egyptian Museum in Cairo.
Moldavite also has a long record of use, and the moldavite guide covers it, but nothing matches a royal Egyptian jewel.
How do prices compare?
Moldavite costs more per gram. Supply is limited to one strewn field, demand from crystal buyers is strong, and large clean pieces are rare, so prices climb steeply with size and with a well-preserved etched surface. That demand is also why fakes are common. Libyan desert glass is usually cheaper per gram at small sizes, is available in larger pieces, and is far less often faked, although cut and polished pieces deserve the same scrutiny as any glass. "African moldavite" is a sales name for manufactured glass, not for Libyan desert glass and not for moldavite.
In crystal traditions, moldavite is linked with transformation and Libyan desert glass with clarity and the solar plexus; these are beliefs, and they do not change how either glass is identified or valued.
Which should you buy?
- Choose moldavite for the green color, the sculpted surface texture and the Ries story. Buy from sellers who state the locality (Czech Republic, usually South Bohemia) and photograph the surface closely.
- Choose Libyan desert glass for size and value, for the Egyptian archaeology connection, or as the honest alternative when someone offers "African moldavite".
- Add a piece of obsidian if you want a three-way comparison: a volcanic glass, a tektite and an impact glass side by side make the differences obvious.
Buying moldavite and Libyan desert glass here
Read listings for color words that match the material, a stated locality, and photos of the natural surface rather than only the polished face. Small raw pieces are the best learning specimens, because the surface carries most of the evidence.
- Moldavite: raw green moldavite, the piece to check for the etched, sculpted skin described above.
- Libyan Desert Glass: natural pale yellow Saharan glass, inexpensive enough to keep beside the moldavite for the color and surface comparison.
- Black Obsidian Crystal Sphere Polished Volcanic Glass: a volcanic glass for the third corner of a natural glass set, showing how a glass with no impact history looks when polished.
Digital Towns Market
Moldavite and Libyan desert glass in stock
Frequently asked questions
Is Libyan desert glass the same as moldavite?
No. Both are natural glasses made by meteorite impacts, but moldavite comes from the Ries impact in Germany about 15 million years ago and is green, while Libyan desert glass formed in the Egyptian Sahara about 29 million years ago and is pale yellow, nearly pure silica.
Is Libyan desert glass a type of moldavite?
No. The name moldavite is reserved for glass from the Ries impact strewn field in Central Europe. Libyan desert glass is a separate impact glass from a different event and continent. Pieces sold as "African moldavite" are usually manufactured glass rather than either material.
Which is rarer, moldavite or Libyan desert glass?
Large moldavite is rarer: the International Gem Society lists 235 g as the largest known moldavite, against 4,500 g for Libyan desert glass. Fine small pieces of both are available, but moldavite supply is tighter and its prices higher.
Where was the Libyan desert glass crater?
Nobody knows yet. Zircon grains in the glass show it was made by a meteorite impact rather than an airburst, but no source crater has been identified. It may be buried beneath the dunes of the Great Sand Sea or eroded beyond recognition.
Can Libyan desert glass be faceted?
Yes. Clean pieces are cut into faceted gems and cabochons, and the IGS marks it among the tektite materials that lapidaries have faceted. Most material is cloudy or streaked, so clean faceted stones are uncommon.
Sources
- International Gem Society, Tektite Value, Price, and Jewelry Information: https://www.gemsociety.org/article/tektite-jewelry-and-gemstone-information/
- International Gem Society, Moldavite Value, Price, and Jewelry Information: https://www.gemsociety.org/article/moldavite-jewelry-and-gemstone-information/
- Geology.com, Moldavite: https://geology.com/gemstones/moldavite/
- The Conversation, How we solved the mystery of Libyan desert glass (Aaron J. Cavosie, 2019): https://theconversation.com/how-we-solved-the-mystery-of-libyan-desert-glass-117253
- Archaeology Magazine, Scarab From Space (2019): https://archaeology.org/issues/september-october-2019/digs-discoveries/trenches-egypt-tut-desert-glass
- Aramco World, Desert Glass: An Enigma (Olsen and Underwood, 1979): https://archive.aramcoworld.com/issue/197905/desert.glass-an.enigma.htm