metamorphic
Fulgurite
Fulgurite (Lechatelierite), amorphous SiO2
Hardness: 6.5 (Mohs); Color: Dark grey to brown/black exterior, light interior; Luster: Vitreous to dull; Crystal structure: Amorphous (glassy); Cleavage: None/Conchoidal fracture; Specific gravity: 2.1 - 2.5
- Hardness
- 6
- Color
- Dark grey to brown/black exterior, light interior
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6.5 (Mohs); Color: Dark grey to brown/black exterior, light interior; Luster: Vitreous to dull; Crystal structure: Amorphous (glassy); Cleavage: None/Conchoidal fracture; Specific gravity: 2.1 - 2.5
Formation & geological history
Formed when lightning hits sandy soil or rock. The massive discharge of electrical energy (at temperatures hitting 1,800°C) instantaneously melts and fuses sand grains into a hollow glass tube. These can be thousands of years old or contemporary depending on local storms.
Uses & applications
Primarily used for geological study, education, and as a unique specimen for mineral collectors. Occasionally used in jewelry or as a decorative 'fossilized lightning' curiosity.
Geological facts
Also known as 'petrified lightning.' They are typically hollow because the rapid expansion of air and water vapor during the strike pushes the molten material outward. The most famous specimens can reach lengths of several meters in deep sandy regions.
Field identification & locations
Identify in the field by looking for brittle, tubular, or crust-like structures that resemble irregular roots but are composed of fused sand/glass. Commonly found in deserts (Sahara, Gobi) or on high-exposure beaches.
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