igneous
Obsidian Arrowhead
Volcanic Glass (Primary composition: SiO2)
Hardness: 5–5.5 Mohs scale; Color: Jet black; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.4
- Hardness
- 5–5
- Color
- Jet black
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5–5.5 Mohs scale; Color: Jet black; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.4
Formation & geological history
Formed through the rapid cooling of felsic lava, which prevents crystal growth. This specimen has been anthropogenically altered through a process called knapping (pressure flaking). Geologically, obsidian is usually younger than a few million years as it eventually devitrifies into quartz.
Uses & applications
Historically used for weaponry and cutting tools due to its ability to produce edges thinner than a steel scalpel. Modernly used in jewelry, ornamental decor, and specialized surgical blades.
Geological facts
Obsidian can be fractured to a thickness of only a few molecules, making it sharp enough to cut through individual cells. Ancient civilizations used it as a high-value trade commodity across great distances.
Field identification & locations
Identified in the field by its distinct shell-like (conchoidal) fractures and sharp edges. This specimen shows clear 'scarch marks' or notches indicative of human shaping. Commonly found in volcanic regions such as Oregon (USA), Mexico, and Iceland.
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