Editor’s note: “Look up at the stars, chase the dream of space.” This piece is co‑created by CAS Voice and Purple Mountain Observatory’s “Tianshiyuan” column to share what’s been happening in the sky lately—in plain language.

 

 Typical Leigong mo ball

If you live in South China, you may have heard of “Leigong mo” (literally “Thunder‑God ink”). For many people there, these glossy black stones are the most tangible bridge between everyday life and the night sky. They wash out of soils after heavy summer storms, get picked up in fields, turned into pendants, and—thanks to legends—are sometimes said to hold special powers. Because they’re affordable, they’ve also become popular collectibles. But where do they really come from?

This article tells the story behind Leigong mo and answers a simple question many newcomers ask: Are tektites rare?

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1) What is “Leigong mo”?

The name first appeared in the 10th century in Liu Xun’s Lingbiao Yilu: “After sudden rain in Leizhou, people find stones like smoky glass in the fields and call them Thunder‑God ink.” Because these black glassy stones often appear after storms, people once thought lightning made them—like ink blocks dropped by a thunder deity.

Today we know them by a more international name: Australasian tektites. Tektites are natural glasses formed when a space rock—an asteroid or comet—slams into Earth. About 0.8 million years ago, such an impact melted surface materials, flung them high into the air at incredible speed, and quenched them into glass as they fell back to Earth. The Australasian tektite event produced an especially large, clean melt; the result is glass that’s very uniform and spread across a huge area.

In short: Leigong mo are pieces of ancient impact‑melt glass.

2) How tektites form (the short, vivid version)

• A fast intruder: A small asteroid or comet hits Earth at tens of thousands of km/h.
• Instant furnace: The shock wave turns surface rocks and soils into a super‑hot, foamy melt—parts even vaporize.
• Giant splash: The melt sprays out at low angles and high speeds (often over 5 km/s), forming droplets, sheets, and blobs.
• Air‑hardening: These red‑hot splashes race through the air. Their outsides chill to glass, trapping flow lines and bubbles.
• Final shapes: Gravity, spin, and air drag sculpt them into spheres, dumbbells, teardrops, discs—and, if they briefly leave the atmosphere and re‑enter, into ablated, streamlined forms.
• Rain of glass: They fall back over areas ranging from local to continental scales, creating a “strewn field.”

 

 

 

• How tektite form

That’s the life story of a tektite—from rock to sky to rock again—in minutes.

3) What do they look like?

Australasian tektites show shape patterns tied to distance from the impact:

• Muong Nong‑type (layered blocks): Closer to the source. Usually big, sometimes over 10 kg. Found mainly in eastern Thailand, southern Laos, and central Vietnam. China’s Hainan has these too.

▲Figure 1 Field occurrence of Muong Nong-type tektite.

 

• Splash forms: Farther from the source and spread the widest. Small to medium pieces (grams to hundreds of grams) with diverse shapes—spheres, ovals, dumbbells, discs, teardrops. Common in Guangdong and Guangxi.

Cute Splash Leigongmo In Guangdong,China

click pic get this item listing

 

• Ablated forms: Pieces that briefly exited high into the atmosphere and got reshaped on the way back—smooth, aerodynamic “flow” surfaces.
• Microtektites: Tiny spheres or teardrops under 1 mm, often found in marine sediments very far from the impact.

Figure 2 Common types of tektites: Muong Nong-type (left) (image from the internet), splash-form and ablation-type tektites (center) [2], and microtektites (right).

Even without the pictures, you can imagine them: glossy, jet‑black glass with pitted, matte skins and silky interior glass.

4) Where are they found?

The Australasian strewn field runs from southern China’s coasts through Southeast Asia to Australia and even Antarctica. It covers more than 10% of Earth’s surface—the most widespread tektite field we know.

If they’re so widespread, are tektites rare? The answer depends on where you are.

• In Southeast Asia and South China, farmers and collectors have found them for decades. In those places, they feel “common” to locals.
• Outside those regions, natural finds are scarce. In Europe, the Americas, or most of Africa, tektites from this event don’t naturally occur in the ground, so collectors rely on imports or on local tektites from other, much smaller events.

Figure 3 Distribution area of the Australasian tektite strewn field.

 

5) So… are tektites rare?

• Regionally abundant, globally scarce: In the core regions of the strewn field, you can still find them with effort. Elsewhere, they’re genuine curiosities.
• Non‑renewable: The event happened once, 800,000 years ago. No fresh “supply” is being made. Unlike ores that can be re‑mined or materials that can be manufactured, tektites are a one‑time gift from a single cosmic splash.
• Shrinking availability: Over decades of collecting, easy surface finds became fewer. Fields get built over, soils get moved, and the “low‑hanging fruit” is gone. Market stock increasingly comes from old finds and secondary sales.
• Collectible potential: Because they’re finite and portable—each with unique shape and flow textures—good specimens tend to hold or increase value, especially uncommon forms, large sizes, and well‑documented provenance. For people outside Southeast Asia and South China, they’re a “rare treasure” that’s getting harder to source.

In short: For newcomers worldwide, yes—tektites are rare in everyday life. Even within the strewn field, they’re non‑renewable and steadily harder to find, which is why thoughtful collecting and scientific documentation matter.

6) Where is the crater?

Everyone—hobbyists and scientists alike—wants to know where the impact happened. For the Australasian event, the “home crater” has been a kind of Holy Grail. Most evidence points to somewhere around the Indochina Peninsula, but the exact location remains unconfirmed. You’ll find a friendly deep‑dive for crater enthusiasts right after this article.

 

7) Takeaway

• Leigong mo = Australasian tektites, born from a massive impact ~800,000 years ago.
• They form when Earth’s surface briefly turns to airborne melt and quenches into glass.
• Shapes tell their flight stories; locations hint at distance from the source.
• They’re non‑renewable, increasingly hard to find on the ground, and prized well beyond their home regions.

Acknowledgment

Thanks to Prof. Xiaozhiyong (Sun Yat‑sen University) for support during writing.

References (friendly list)

1. Tada, T. et al., 2020, Progress in Earth and Planetary Science, 7(1), 1–15.
2. Stauffer, M. R., Butler, S. L., 2010, Earth, Moon, and Planets, 107, 169–196.
3. Rochette, P. et al., 2018, Geology, 46(9), 803–806.
4. Jourdan, F. et al., 2019, Meteoritics & Planetary Science, 54(10), 2573–2591.
5. Tada, T. et al., 2022, Meteoritics & Planetary Science, 57(10), 1879–1901.
6. Sieh, K. et al., 2020, Proceedings of the National Academy of Sciences, 117(3), 1346–1353.
7. Mizera, J. et al., 2016, Earth‑Science Reviews, 154, 123–137.
8. Whymark, A., 2021, Thai Geoscience Journal, 2, 1–29.