Fulgurites are natural hollow glass tubes formed when lightning strikes silica-rich sand or soil, instantly melting it into glassy formations. They are characteristically fragile with a rough, sandy exterior and a smooth, vitrified interior lining. Rockhounders typically hunt for them in large sand dune fields or coastal sandy areas following severe lightning storms.

Hardness

6.5-7

Mohs

Luster

Glassy

Streak

White

Transparency

Translucent

mineraluncommon

Fulgurite

Also: Petrified Lightning

Hardness: 6.5-7
Luster: Glassy
Streak: White
Transparency: Translucent

Is this fulgurite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch fulgurite with a known reference. Fulgurite sits at Mohs 6.5-7 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Fulgurite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Fulgurite typically shows a glassy luster.
4
Match the color range
Compare against the expected color range: white, gray, tan, brown, black.
5
Look at form & habit
Crystal system: amorphous. Typical habit: tubular, branching, root-like.

Often confused with

Fulgurite vs. its common look-alikes — and how to tell them apart in the field.

igneous

Obsidian

Mohs 5-6

How to tell apart: Luster reads glassy on Fulgurite and vitreous on Obsidian.

How to tell apart: Luster reads glassy on Fulgurite and vitreous on Lechatelierite.

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Often found alongside fulgurite

Minerals reported to co-occur with fulgurite. Spotting these in float or country rock is a strong cue you are in the right ground.

Quartz
mineral · Mohs 7

All properties

Chemical formula: SiO₂
Mohs hardness: 6.5-7
Density: 2.1-2.6 g/cm³
Colors: White Gray Tan Brown Black
Streak: White
Luster: Glassy
Transparency: Translucent
Crystal system: Amorphous
Crystal habit: Tubular, Branching, Root-like
Cleavage: None
Rarity: Uncommon
Uses: Collector, Scientific Research
Host rock: Loose Sand Dunes or Silica-rich Soil
Typical price: $20-200 depending on length and branching complexity

Where rockhounds find fulgurite

Classic worldwide localities

Sahara Desert
Gobi Desert
Florida, USA
Arizona, USA

Field-hunting tip

Look in loose sand dunes or silica-rich soil country — that is the host setting where fulgurite typically forms. If you start seeing quartz, sand in float, you are in the right ground. Field specimens usually show a tubular, branching, root-like habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify fulgurite?+

Mohs hardness is 6.5-7. It typically shows a glassy luster. The streak is white. Common colors include white, gray, tan, brown.

Where is fulgurite found?+

Notable localities include Sahara Desert; Gobi Desert; Florida, USA; Arizona, USA.

How much is fulgurite worth?+

Typical asking prices fall in the range of $20-200 depending on length and branching complexity. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like fulgurite?+

Fulgurite is most often confused with Obsidian, Lechatelierite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with fulgurite?+

Fulgurite commonly co-occurs with Quartz, Sand. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does fulgurite form in?+

Fulgurite typically forms in loose sand dunes or silica-rich soil. Working float back to the host body is the standard way to chase a fresh occurrence.

What is fulgurite used for?+

Fulgurite is used in collector, scientific research.

Find fulgurite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.