metamorphic
Fulgurite (Sand-tube)
Fulgurite (Lechatelierite-rich fused sand)
Hardness: 5.5 to 7. Color: Tan, reddish-brown, or grey. Luster: Dull/gritty exterior, glassy interior. Crystal structure: Amorphous (glass). Cleavage: None. Specific gravity: 2.2-2.5.
- Hardness
- 5
- Color
- Tan, reddish-brown, or grey
- Luster
- Dull/gritty exterior, glassy interior
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Physical properties
Hardness: 5.5 to 7. Color: Tan, reddish-brown, or grey. Luster: Dull/gritty exterior, glassy interior. Crystal structure: Amorphous (glass). Cleavage: None. Specific gravity: 2.2-2.5.
Formation & geological history
Formed when lightning strikes the ground, instantly melting and fusing sand or soil into a tube following the path of the electric discharge. These can form in sandy soils like those found in the Piedmont or Coastal Plain regions of North Carolina (approx. 35.9°N, 78.9°W).
Uses & applications
Used primarily as scientific specimens to study prehistoric lightning patterns and by collectors of oddities and geological rarities. Also used in some unique jewelry pieces.
Geological facts
Fulgurites are often called 'petrified lightning.' The temperature required to form them is approximately 1,800 degrees Celsius (3,270 degrees Fahrenheit). They are essentially natural glass tubes.
Field identification & locations
Look for hollow, tube-like structures with a rough, sand-encrusted exterior and a smooth or bubbly glassy lumen. They are often found in sandy areas or after large storms in locations with suitable soil resistivity.
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