igneous
Black volcanic glass or basalt pendant
Likely basalt (fine-grained mafic rock), possibly obsidian (volcanic glass)
AI-generated identification · may be incorrectOpaque black, rough-to-slightly vitreous luster, irregular vesicles and fracture surfaces; basalt hardness about 5–6 Mohs, obsidian about 5–5.5. No visible crystals or cleavage; the attached metal loop is manufactured, but the pendant appears geological.
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Physical properties
Opaque black, rough-to-slightly vitreous luster, irregular vesicles and fracture surfaces; basalt hardness about 5–6 Mohs, obsidian about 5–5.5. No visible crystals or cleavage; the attached metal loop is manufactured, but the pendant appears geological.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface; obsidian forms when silica-rich lava quenches into glass. The specimen’s geological age cannot be determined visually; similar materials range from recent volcanic flows to rocks millions of years old.
Uses & applications
Used as a decorative pendant, carving material, aggregate, roadstone, and construction rock; obsidian is also collected and used for sharp-edged tools and jewelry.
Geological facts
The porous texture favors basalt or scoria over true obsidian, which is usually glassy and conchoidally fractured. A streak test, density measurement, and close inspection for microscopic crystals would help distinguish them.
Field identification & locations
Common in volcanic regions, including Hawaii, Iceland, Japan, Mexico, and the western United States. Basalt is dense and dull with tiny crystals; scoria is noticeably lightweight and vesicular, while obsidian is glassy with curved fracture surfaces.
