mineral

Black tourmaline (schorl), possibly rough obsidian

Schorl tourmaline: NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄; visual confirmation is limited

AI-generated identification · may be incorrect

Black, opaque, vitreous to resinous luster; Mohs hardness 7–7.5; commonly prismatic with lengthwise striations and no prominent cleavage. The blocky, dark specimen could also be glassy obsidian, which has conchoidal fracture and hardness about 5–5.5.

Identified August 20, 2026More mineral →

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Physical properties

Formation & geological history

Tourmaline commonly crystallizes in granitic pegmatites and hydrothermal veins during late igneous activity; obsidian is rapidly cooled volcanic rhyolitic lava, generally Quaternary to older Cenozoic. Age cannot be determined from the photograph.

Uses & applications

Tourmaline is collected and occasionally used as a gemstone; gem-quality varieties are faceted, while black schorl is mainly ornamental. Obsidian is used for carvings, tools, cabochons, and decorative objects.

Geological facts

Tourmaline is strongly piezoelectric and develops electric charge when heated or compressed. Obsidian is natural volcanic glass rather than a crystalline mineral.

Field identification & locations

Look for tourmaline’s striated prismatic faces and uneven fracture; test only with permission using hardness and streak methods. Common sources include Brazil, Afghanistan, Pakistan, Maine, and California; obsidian occurs in volcanic regions worldwide.