mineral

Black tourmaline (likely schorl), polished cabochon

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

AI-generated identification · may be incorrect

Typically black, opaque, and vitreous to resinous with no visible crystal faces here because it is polished; Mohs hardness 7–7.5, poor cleavage, trigonal crystal structure, and specific gravity about 3.0–3.3. The mounted stone appears rectangular with rounded corners and reflective polish.

Identified August 16, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in granite pegmatites and hydrothermal veins when boron-rich fluids crystallize; most specimens are Paleozoic to younger, though age depends on locality. Common sources include Brazil, Afghanistan, Pakistan, Madagascar, and the United States.

Uses & applications

Used as a durable ornamental and jewelry gemstone, especially in rings, pendants, and cabochons; coarse tourmaline is also collected as mineral specimens. This piece is set in a metal jewelry mount.

Geological facts

Schorl is the most common tourmaline variety and owes its black color largely to iron. Tourmaline is strongly piezoelectric and can develop electrical charge when heated or compressed.

Field identification & locations

Identify by its deep black color, high polish, moderate weight, hardness, and lack of cleavage; rough material commonly shows striated prismatic crystals. A definitive identification would require testing because black spinel, onyx, obsidian, and other stones can look similar.