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Tektites are natural glass objects, typically black, dark brown, or dark green, formed from the impact of large meteorites on Earth's surface. They are characterized by their distinctive aerodynamic shapes (e.g., spheres, dumbbells, buttons, teardrops) and often exhibit surface sculpturing, pitting, and flow lines resulting from atmospheric re-entry. Their composition is primarily silica-rich, similar to terrestrial rocks, but they are virtually water-free and lack crystalline structure.
How to Identify
- Color
- Typically black, dark brown, or dark green. Rarely yellowish-green (moldavites).
- Luster
- Vitreous (glassy) to dull.
- Texture
- Smooth to highly sculptured, often with pits, grooves, and flow lines. Can be aerodynamic in shape.
- Crystal Form
- Amorphous (no crystal structure).
- Cleavage
- None, exhibits conchoidal fracture.
- Geological Environment
- Found in strewn fields associated with large meteorite impact events, often in unconsolidated sediments like sands and gravels.
Key Facts
- Hardness: 5.5-6.5 on Mohs scale
- Specific Gravity: 2.3-2.8 g/cm3
- Crystal System: Amorphous
- Color: Black, dark brown, dark green (rarely yellowish-green)
- Luster: Vitreous to dull
- Transparency: Opaque to translucent (especially on thin edges)
- Fracture: Conchoidal
- Cleavage: None
- Composition: Primarily silica (SiO₂, 65-80%), with varying amounts of Al₂O₃, FeO, MgO, CaO, K₂O, Na₂O, and TiO₂. Characteristically very low water content (<0.02 wt%).
Quick Check
- Color: Black, dark brown, dark green
- Luster: Vitreous to dull
- Streak: None (glass)
Physical Characteristics
- Crystal Habit: Amorphous, typically found as aerodynamically shaped objects (spheres, dumbbells, teardrops, buttons, lenses, irregular fragments).
- Cleavage Type: None
- Fracture Type: Conchoidal, producing sharp, curved surfaces.
- Tenacity: Brittle
- Luster Type: Vitreous (glassy) to dull.
Formation
Tektites are formed from terrestrial rock melted by the hypervelocity impact of large meteorites. The molten material is ejected into the atmosphere, cools rapidly, and solidifies into glass before falling back to Earth.
Usage
Historically, tektites have been used by indigenous cultures for tools, amulets, and ornamental purposes. Today, they are primarily collected by enthusiasts and used in jewelry.
Age Distribution
Ranges from approximately 0.78 million years (Australasian tektites) to 35 million years (North American tektites) and 14.7 million years (Central European tektites).
Where to Find
Australasian Strewn Field
Covers Southeast Asia, Australia, and Antarctica. Source of black tektites (australites, indochinites, philippinites) and some moldavite-like glasses. Age: ~0.78 Ma.
Central European Strewn Field
Primarily Czech Republic (Bohemia and Moravia) and Germany. Source of green moldavites. Age: ~14.7 Ma.
North American Strewn Field
Southeastern United States (Georgia, Texas) and Caribbean Sea. Source of georgiaites and bediasites. Age: ~35 Ma.
Ivory Coast Strewn Field
West Africa (Ivory Coast). Source of ivorites. Age: ~1.07 Ma.
Finding Tips
Research Strewn Fields
Focus your search on known tektite strewn fields. These are vast areas, but specific localities within them are more productive.
Look in Sedimentary Deposits
Tektites are typically found in unconsolidated sediments like river gravels, alluvial plains, and weathered soils, rather than in bedrock.
Examine Surface Features
Look for characteristic aerodynamic shapes, surface sculpturing, pitting, and flow lines. These features distinguish tektites from ordinary terrestrial rocks or volcanic glass.
Check for Translucency
While often appearing opaque black, thin edges or small fragments of tektites can be translucent, revealing dark brown, green, or yellowish-green hues when held up to a strong light.
Test for Magnetism (Rare)
Some tektites may contain microscopic metallic spherules (nickel-iron) from the impactor, which can cause a very weak magnetic attraction, though this is not a primary identification method.
Similar Rocks
Obsidian
Obsidian
Also known as: Volcanic Glass
Impact Glass
Impactite
Also known as: Impact Melt Glass
Fulgarite
Fulgarite
Also known as: Fulgurite
Scientific Classification
- Mineral Class
- Not a mineral (amorphous)
- Group
- Natural Glass (Impactite)
- Crystal System
- Amorphous
- Chemical Formula
- Variable, primarily SiO₂ with other oxides (e.g., Al₂O₃, FeO, MgO)
- Composition
- Silica-rich glass, formed from melted terrestrial rock. Distinctly low water content compared to volcanic glasses.
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