mineral

Tumbled black tourmaline

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

AI-generated identification · may be incorrect

Typically black to brownish-black with vitreous to resinous luster; Mohs hardness 7–7.5, trigonal crystal structure, poor cleavage, and specific gravity about 3.0–3.3. The rounded surface indicates tumbling or natural water abrasion.

Identified August 16, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in granitic pegmatites and hydrothermal veins as boron-rich magma cools, commonly during the Precambrian to Cenozoic. It is widespread in metamorphic and igneous terrains.

Uses & applications

Used as a durable ornamental and lapidary stone, in cabochons, beads, carvings, and mineral collections; industrial tourmaline has limited use in pressure-sensitive electrical applications.

Geological facts

Schorl is the most common tourmaline species and may show strong piezoelectric and pyroelectric behavior. Brown translucency at the edge can reflect internal zoning or thin sections.

Field identification & locations

Identify it by its black color, rounded triangular/prismatic form, high hardness, and occasional lengthwise striations; common sources include Brazil, Afghanistan, Madagascar, Pakistan, and the United States. A gemological test is needed to distinguish it from obsidian or black glass.