mineral
Black polished stone, likely black tourmaline or obsidian
Possibly schorl tourmaline, NaFe3Al6(BO3)3Si6O18(OH)4, or volcanic glass (obsidian), SiO2-rich
AI-generated identification · may be incorrectDark opaque to translucent material with a glassy-to-subvitreous luster; identification is uncertain because the specimen is enclosed and the image is blurred. Tourmaline has Mohs hardness 7–7.5 and prismatic crystal structure; obsidian has hardness about 5–5.5 and no crystal structure.
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Physical properties
Dark opaque to translucent material with a glassy-to-subvitreous luster; identification is uncertain because the specimen is enclosed and the image is blurred. Tourmaline has Mohs hardness 7–7.5 and prismatic crystal structure; obsidian has hardness about 5–5.5 and no crystal structure.
Formation & geological history
Black tourmaline crystallizes in hydrothermal veins and granitic pegmatites, while obsidian forms when silica-rich lava cools rapidly; both are geologically young to ancient depending on locality.
Uses & applications
Tourmaline is collected, used as a gemstone, and sometimes in electrical applications; obsidian is used for carvings, jewelry, ornaments, and historically sharp tools.
Geological facts
Black tourmaline commonly shows longitudinal striations and may attract lightweight particles when heated; obsidian typically breaks with conchoidal, razor-sharp fractures.
Field identification & locations
Check for prismatic striations, crystal faces, and lack of conchoidal fracture for tourmaline; a uniform glassy body with curved fracture favors obsidian. Common sources include Brazil, Afghanistan, Madagascar, Mexico, and the western United States.
