mineral

Black tourmaline (schorl)

Schorl, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

AI-generated identification · may be incorrect

Black to dark brown, strongly striated, elongated prismatic crystals with vitreous-to-submetallic luster; Mohs hardness 7–7.5, trigonal crystal system, poor cleavage, specific gravity about 3.0–3.3. The specimen’s grooved, columnar form is characteristic of tourmaline.

Identified October 10, 2026More mineral →

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Physical properties

Formation & geological history

Typically crystallizes in granitic pegmatites and boron-rich hydrothermal veins as magma cools; tourmaline occurs in rocks of many ages, so the specimen’s age cannot be determined from appearance alone.

Uses & applications

Collected as a mineral specimen and occasionally used in jewelry; black tourmaline is also sold as a decorative stone. It has limited major industrial use compared with some other tourmaline varieties.

Geological facts

Tourmaline crystals can develop electrical charge when heated or compressed (pyroelectric and piezoelectric effects).

Field identification & locations

Look for long, deeply lengthwise-striated black prisms and hardness sufficient to scratch glass; confirmatory identification may require mineral testing. Common sources include Brazil, Pakistan, Afghanistan, and parts of the United States.