Igneous
Obsidian Arrowhead
Volcanic Glass (70% or more SiO2)
Hardness: 5-5.5 (Mohs scale); Color: Jet black to dark grey; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35–2.6
- Hardness
- 5-5
- Color
- Jet black to dark grey
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Jet black to dark grey; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35–2.6
Formation & geological history
Formed from rapidly cooling felsic lava that solidifies without sufficient time for crystal growth. Found in geologically recent volcanic areas (mostly Pliocene to Holocene). Common in the Pacific Northwest, Mexico, and Iceland.
Uses & applications
Historically used for cutting tools, scrapers, and arrowheads. Currently used in jewelry, decorative items, and high-precision surgical scalpel blades.
Geological facts
Obsidian fractures with an edge much thinner and sharper than a steel scalpel, down to a single molecule of thickness. It was a primary trade commodity in the ancient world, often called 'Black Gold' by Mesoamerican civilizations.
Field identification & locations
Identify in the field by its distinct glassy appearance, lack of grain, and sharp, curved edges. This specific specimen has been worked (knapped) by humans into a corner-notched projectile point shape.
