mineral

Raw tourmaline crystal (probable schorl)

Tourmaline group; likely schorl, NaFe3+Al6(BO3)3Si6O18(OH)4

AI-generated identification · may be incorrect

Black to dark green, vitreous luster, striated prismatic crystal faces and uneven fracture; Mohs hardness 7–7.5, trigonal crystal system, poor cleavage, specific gravity about 3.1–3.3. The apparent green zones may indicate elbaite or mixed tourmaline composition.

Identified August 10, 2026More mineral →

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Physical properties

Formation & geological history

Forms mainly in granitic pegmatites and hydrothermal veins during late-stage crystallization, commonly in Precambrian to younger igneous terrains. The image alone cannot establish a precise age or species.

Uses & applications

Tourmaline is used as a gemstone, ornamental mineral, and collector specimen; schorl is also studied for its electrical and piezoelectric properties. Quality transparent colored crystals can be valuable, while opaque rough pieces are usually modestly priced.

Geological facts

Tourmaline crystals often show strong longitudinal striations and can become electrically charged when heated or rubbed (pyroelectric and piezoelectric effects).

Field identification & locations

Look for a three-sided to six-sided striated prism, glassy luster, and resistance to scratching by ordinary steel; a hardness test and specific-gravity or laboratory analysis are needed to distinguish it from amphibole, biotite, or other dark minerals. Common sources include Brazil, Afghanistan, Madagascar, Namibia, and the United States.