mineral
Polished black-and-white tourmaline
Schorl tourmaline, complex borosilicate; commonly black schorl with quartz or feldspar inclusions
AI-generated identification · may be incorrectTypically Mohs 7–7.5, black to dark gray with pale gray/white internal streaks, vitreous luster, and trigonal crystal structure; polished specimens have no visible cleavage and a specific gravity around 3.0–3.3.
Identified More mineral →
Explore Polished black-and-white tourmaline in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically Mohs 7–7.5, black to dark gray with pale gray/white internal streaks, vitreous luster, and trigonal crystal structure; polished specimens have no visible cleavage and a specific gravity around 3.0–3.3.
Formation & geological history
Forms in granitic pegmatites and metamorphic veins as hydrothermal boron-rich fluids crystallize, generally during Precambrian to Phanerozoic tectonic events. Common sources include Brazil, Afghanistan, Madagascar, Namibia, and the United States.
Uses & applications
Used as a gemstone, cabochon, ornamental stone, and mineral specimen; tourmaline is also valued for its piezoelectric and pyroelectric properties. Small polished pieces typically have modest decorative value.
Geological facts
The pale bands may be quartz, feldspar, or another tourmaline zone, so exact identification from the photograph is uncertain. Tourmaline crystals can develop electrical charges when heated or compressed.
Field identification & locations
Identify by its very dark color, strong polish, hardness, and often striated or banded appearance; a streak test, hardness test, and magnification can distinguish it from obsidian or dyed glass. Look for prismatic, longitudinally striated crystals in pegmatites.
