mineral

Black tourmaline (schorl), likely in a crystal aggregate

Schorl, NaFe3Al6(BO3)3Si6O18(OH)4

AI-generated identification · may be incorrect

Opaque black, commonly vitreous to submetallic luster; Mohs hardness 7–7.5; trigonal crystal structure; typically prismatic crystals with strong longitudinal striations and no obvious cleavage. The photographed pieces appear angular and crystalline, though exact identification from an image is not certain.

Identified September 22, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in granitic pegmatites, hydrothermal veins, and metamorphic rocks through boron-rich fluids. Most specimens are Precambrian to Cenozoic, depending on the host deposit.

Uses & applications

Used as a collector mineral and occasionally in jewelry when well-formed; crushed tourmaline has minor industrial and ornamental uses. Ordinary fragmentary material has modest value.

Geological facts

Schorl is the most common tourmaline species and is strongly pleochroic in transparent sections. Tourmaline can become electrically polarized when heated or compressed (pyroelectric and piezoelectric effects).

Field identification & locations

Look for black, striated prismatic crystals, high hardness, and resistance to scratching by steel. At 19.1°N, 72.9°E (Mumbai), basalt and weathered Deccan volcanic rocks are more regionally typical; black basalt or industrial aggregate is a plausible alternative, and the image alone cannot confirm tourmaline.