mineral
Tumbled black tourmaline (likely schorl)
Schorl, sodium–iron tourmaline: NaFe²⁺₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectVery dark brown-black, vitreous to resinous luster, commonly opaque, with an elongated trigonal crystal structure and no obvious cleavage; Mohs hardness 7–7.5, specific gravity about 3.1–3.3. The smooth shape indicates tumbling or polishing, and the brown-golden crust may be matrix or weathering.
Identified More mineral →
Explore Tumbled black tourmaline (likely schorl) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Very dark brown-black, vitreous to resinous luster, commonly opaque, with an elongated trigonal crystal structure and no obvious cleavage; Mohs hardness 7–7.5, specific gravity about 3.1–3.3. The smooth shape indicates tumbling or polishing, and the brown-golden crust may be matrix or weathering.
Formation & geological history
Forms mainly in granite pegmatites and hydrothermal veins during late-stage igneous crystallization, generally in Phanerozoic or older continental crust. Common sources include Brazil, Namibia, Afghanistan, Pakistan, Madagascar, and the United States.
Uses & applications
Used as a collector mineral, ornamental stone, and occasionally in jewelry; tourmaline’s electrical and piezoelectric properties also support technical applications. This specimen appears primarily decorative.
Geological facts
Tourmaline is strongly pleochroic and can become electrically charged when heated or rubbed (the origin of its name, linked to ‘mixed colors’). Schorl is the most common tourmaline species.
Field identification & locations
Identify by its black elongated form, high hardness, lack of cleavage, and often striated prism faces; a glass scratch test and a strong neodymium-magnet response may help, though polishing obscures features. Confirmatory identification requires testing or microscopy.
