mineral

Polished black mineral or volcanic glass fragment

Indeterminate; possibly obsidian or black tourmaline

AI-generated identification · may be incorrect

Dark green-black, highly reflective surface with apparent conchoidal or irregular breakage; hardness likely about 5–7 Mohs. The image is distorted by textured glass and colored reflections, preventing reliable determination of luster, cleavage, crystal structure, or specific gravity.

Identified August 8, 2026More mineral →

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Physical properties

Formation & geological history

If obsidian, it is rapidly cooled silica-rich volcanic lava, generally Quaternary to recent; if tourmaline, it crystallized in granitic pegmatites or metamorphic rocks. Geological age and formation cannot be established from this image.

Uses & applications

Obsidian is used for ornaments, tools, and jewelry; black tourmaline is used as a gemstone and collector mineral. Value depends strongly on confirmed identity, size, transparency, and finish.

Geological facts

The apparent green, red, and blue colors are likely reflections from the surrounding scene rather than the specimen itself. A fresh conchoidal fracture and glassy texture would favor obsidian; prismatic crystal faces and lengthwise striations would favor tourmaline.

Field identification & locations

Common obsidian occurs in volcanic regions such as the western United States, Mexico, Iceland, and Japan; tourmaline is widespread in pegmatites, notably Brazil, Afghanistan, and California. A clear photo outside reflective glass, plus hardness and streak tests, is needed for identification.