metamorphic

Tourmaline-rich schist (likely black tourmaline)

Schist containing schorl, Fe-rich NaFe3Al6(BO3)3Si6O18(OH)4

AI-generated identification · may be incorrect

Dark gray-black, elongated and strongly foliated with a silky to submetallic luster; likely Mohs 7–7.5 for tourmaline, though the schist matrix is softer. Tourmaline is trigonal and commonly shows prismatic crystals with poor cleavage and conchoidal fracture.

Identified September 11, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when boron-rich sedimentary or igneous material underwent regional metamorphism, producing aligned mica and tourmaline; age depends on locality, commonly Paleozoic to Precambrian. The specimen appears naturally elongated, possibly a weathered tourmaline-rich metamorphic fragment.

Uses & applications

Used mainly as a mineral-collecting specimen; black tourmaline is also cut for cabochons and beads, while tourmaline’s piezoelectric properties support limited scientific and electrical applications.

Geological facts

Schorl is the most common tourmaline species and is typically opaque black. Strong striations along crystal faces are a useful diagnostic feature.

Field identification & locations

Look for longitudinal striations, a black or brown-black color, lack of obvious cleavage, and hardness sufficient to scratch glass; a magnet response is generally weak or absent. Common localities include Brazil, Afghanistan, Pakistan, Namibia, Madagascar, and the United States.