igneous
Obsidian (Arrowhead Lithic Tool)
Obsidian (Amorphous Volcanic Glass / SiO2 + inclusions)
Hardness: 5–5.5 Mohs scale; Color: Jet black to smoky translucent; Luster: Vitreous (glassy); Crystal structure: Amorphous (none); Cleavage: Conchoidal fracture; Specific gravity: 2.3–2.6.
- Hardness
- 5–5
- Color
- Jet black to smoky translucent
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5–5.5 Mohs scale; Color: Jet black to smoky translucent; Luster: Vitreous (glassy); Crystal structure: Amorphous (none); Cleavage: Conchoidal fracture; Specific gravity: 2.3–2.6.
Formation & geological history
Formed through the extremely rapid cooling of felsic (silica-rich) lava, preventing crystal growth. It typically occurs in geologically young volcanic areas (Pliocene to Holocene) because it eventually devitrifies into crystalline rock over time.
Uses & applications
Historically used for prehistoric tools (arrowheads, scrapers, knives) due to its razor-sharp edges. Modernly used in high-precision scalpel blades, jewelry, and as a popular collector's mineral.
Geological facts
Obsidian can produce a cutting edge that is exponentially thinner and sharper than a steel scalpel, down to molecular widths. This specific specimen is an artifact known as a 'projectile point,' likely created via flint knapping.
Field identification & locations
Identify in the field by its distinct glassy appearance, smooth curved (conchoidal) fracture surfaces, and translucent edges when held to the light. Commonly found in Iceland, Italy, Mexico, and the Western United States (Oregon/California).
