Fulgurite
Fulgurite is natural glass (lightning-fused sediment), (lechatelierite, fused SiO₂). In the hand, it rates 5 to 6 (thin, fragile walls) on the Mohs scale, and it runs sandy tan and gray. Hollow, sand-crusted branching tubes with glassy interiors, the fossilized path of a lightning bolt through sand or soil.
The geology.
Fulgurite carries the formula (lechatelierite, fused SiO₂). It belongs to the amorphous system. The trade files it under natural glass (lightning-fused sediment).
It sits at 5 to 6 (thin, fragile walls) on the Mohs scale. The surface reads glassy inside, sandy-crusted outside. Light behaviour is translucent glassy interior. Specific gravity runs 1.8 to 2.5 (hollow, variable). The streak is white. It breaks with brittle, hollow tubes snap easily.
Hollow, sand-crusted branching tubes with glassy interiors, the fossilized path of a lightning bolt through sand or soil.
Common cuts are hollow branching tubes, crusted root-like forms or fragments in display boxes.
The origins.
Beach dunes and sandy highlands struck by lightning, Sahara, Florida and Great Lakes dunes (USA), Australia.
On value, the database notes: mid-range; large intact natural branches are prized.
Traditional associations.
In energy work traditions, associated with sudden insight and channeling high-voltage inspiration.
Included for completeness. Tradition is worth knowing about, and it is worth keeping separate from the mineralogy.
Spotting the real thing.
Hollow, sand-crusted branching tubes with glassy interiors, the fossilized path of a lightning bolt through sand or soil.
Artificial fulgurites made with welders or downed power lines circulate widely, perfect long tubes at low prices warrant skepticism.
| Looks like | How to tell them apart |
|---|---|
| Man-made 'fulgurite' (furnace or arc-made) | Faked tubes are suspiciously long, intact, uniform, and abundant; natural ones are fragile, irregular, and branch organically |
| Worm tubes/concretions | Concretion tubes are sediment-cored, not glass-lined |
| Slag drips | Slag is solid, bubbly glass without a sand-grain crust |
At-home tests.
These checks cost nothing. Daylight, a 10x loupe and a little patience are the whole kit for fulgurite.
| Test | What you should see |
|---|---|
| By eye | Glassy smooth interior with rough sand-grain exterior |
| By eye | Hollow or partly hollow cross-section |
| By eye | Featherlight and fragile for its size |
Anything that scratches, burns or dissolves the piece is a lab job. Get it appraised rather than testing it apart.
Care & handling.
At 5 to 6 (thin, fragile walls) on the Mohs scale it handles careful wear but scratches against quartz and dust. Store it separately and take rings off before rough work.
It breaks with brittle, hollow tubes snap easily, which is worth knowing before you set it or drop it.
Warm water and a soft cloth clean almost everything. Ultrasonic tanks, steamers and household cleaners are where pieces get ruined.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is (lechatelierite, fused SiO₂). Crystal system: Amorphous. Specific gravity: 1.8 to 2.5 (hollow, variable). Streak: White. Cleavage and fracture: Brittle, hollow tubes snap easily.
How it reaches the market
Beach dunes and sandy highlands struck by lightning, Sahara, Florida and Great Lakes dunes (USA), Australia.
What it gets confused with
Man-made 'fulgurite' (furnace or arc-made): Faked tubes are suspiciously long, intact, uniform, and abundant; natural ones are fragile, irregular, and branch organically. Worm tubes/concretions: Concretion tubes are sediment-cored, not glass-lined. Slag drips: Slag is solid, bubbly glass without a sand-grain crust.
What it is worth
Mid-range; large intact natural branches are prized.
Where buyers get caught
Artificial fulgurites made with welders or downed power lines circulate widely, perfect long tubes at low prices warrant skepticism.
One more thing
A bolt's core hits ~30,000 K, hotter than the Sun's surface, turning sand to glass in microseconds and freezing the strike's shape forever.
An education-first guide.
No product links here. We do not sell fulgurite, and a guide that only covers our own shelves would not be much of a guide.
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