igneous
Obsidian
Volcanic Glass (Amorphous Silicon Dioxide)
Hardness: 5.5 on the Mohs scale, Color: Pitch black, dark brown, or gray (sometimes with sheen), Luster: Vitreous (glassy), Crystal Structure: Amorphous (non-crystalline), Cleavage: Conchoidal, Specific Gravity: 2.35-2.60
- Hardness
- 5
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Physical properties
Hardness: 5.5 on the Mohs scale, Color: Pitch black, dark brown, or gray (sometimes with sheen), Luster: Vitreous (glassy), Crystal Structure: Amorphous (non-crystalline), Cleavage: Conchoidal, Specific Gravity: 2.35-2.60
Formation & geological history
Formed as an extrusive igneous rock when felsic lava extruded from a volcano cools rapidly with minimal crystal growth.
Uses & applications
Widely used for jewelry, decorative objects, metaphysical healing, and historically for cutting tools, arrowheads, and blades due to its extremely sharp conchoidal fracture.
Geological facts
Because it is a glass and not a true mineral, obsidian does not have a crystalline structure. It breaks with extremely sharp edges that can be finer than surgical scalpels.
Field identification & locations
Easily identified by its dark, glassy appearance and characteristic conchoidal fracture. Found worldwide in areas with past volcanic activity, such as the western United States, Mexico, and Italy.
