Polished black-and-golden tourmaline

Mohs hardness 7–7.5; black, brown, and honey-gold coloration with vitreous luster. Trigonal crystal structure; typically lacks obvious cleavage, with uneven fracture and specific gravity about 3.0–3.3.

Forms in boron-rich hydrothermal veins, pegmatites, and metamorphic rocks during late-stage crystallization, commonly from Paleozoic to younger geological settings. The specimen is tumbled or polished, obscuring its natural crystal form.

Used as a gemstone, cabochon, ornamental stone, and collector material; tourmaline crystals are also valued for their piezoelectric and pyroelectric properties.

The black portion is likely schorl, while the brown-golden zone may be dravite or iron-rich transitional tourmaline. Tourmaline can become electrically charged when heated or rubbed.

Identify by strong glassy luster, high hardness, elongated striated crystals in natural specimens, and possible color zoning; black tourmaline is common in Brazil, Afghanistan, Pakistan, Madagascar, and the United States. A polished surface and sharp color boundary may indicate a cut or composite piece, so exact identification requires testing.