igneous
Polished black stone, likely obsidian or dark basalt
Volcanic glass (obsidian), possibly basalt; exact identification requires testing
AI-generated identification · may be incorrectVery dark gray to black, strongly vitreous and partly waxy luster, with irregular pale mineral inclusions and conchoidal-looking fractures. Obsidian hardness is about 5–5.5 Mohs, lacks crystal structure and cleavage; basalt is about 6 Mohs and fine-grained crystalline.
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Physical properties
Very dark gray to black, strongly vitreous and partly waxy luster, with irregular pale mineral inclusions and conchoidal-looking fractures. Obsidian hardness is about 5–5.5 Mohs, lacks crystal structure and cleavage; basalt is about 6 Mohs and fine-grained crystalline.
Formation & geological history
An igneous volcanic specimen formed from rapidly cooled silica-rich lava if obsidian, or cooled mafic lava if basalt; likely Quaternary to older volcanic material. Common sources include Mexico, the western United States, Iceland, and Turkey.
Uses & applications
Used for carvings, cabochons, ornaments, and collectible polished stones; obsidian historically served for extremely sharp tools and blades. Basalt is widely used as aggregate, dimension stone, and road material.
Geological facts
Obsidian can show snowflake, sheen, or rainbow effects from inclusions and microscopic flow structures. The pictured specimen appears polished and may be a mixed or brecciated volcanic rock rather than pure obsidian.
Field identification & locations
Check for sharp conchoidal fracture, glassy translucence at thin edges, and absence of visible grains for obsidian; visible interlocking grains and a denser, duller surface favor basalt. A streak, hardness, and specific-gravity test would help distinguish them.
