mineral
Polished black stone, possibly black tourmaline
Uncertain from the image; possibly schorl, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectSmall, dark, rounded and polished specimen with a subdued luster; crystal structure, hardness, and specific gravity cannot be determined reliably from the image. If schorl, hardness is about 7–7.5 Mohs and its crystals are trigonal.
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Physical properties
Small, dark, rounded and polished specimen with a subdued luster; crystal structure, hardness, and specific gravity cannot be determined reliably from the image. If schorl, hardness is about 7–7.5 Mohs and its crystals are trigonal.
Formation & geological history
Black tourmaline forms in boron-rich granitic pegmatites and metamorphic rocks; such deposits occur across many geological ages. The specimen appears shaped or polished by humans.
Uses & applications
May be sold as a decorative or collectible stone; tourmaline is also used in jewelry.
Geological facts
The image alone does not show diagnostic crystal faces or other features that confirm tourmaline; other dark minerals or polished stones could look similar.
Field identification & locations
Identification would require close inspection for tourmaline’s lengthwise striations, or tests of hardness and density. Tourmaline occurs worldwide, notably in Brazil, Afghanistan, Pakistan, and the United States.
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Sandstone (with potential mineral staining/concretions)
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Tumbled granite
Granite, a coarse-grained felsic intrusive igneous rock
igneous
Pegmatite with Tourmaline and Quartz
Igneous Pegmatite
igneous
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Granite
Granite (Phaneritic intrusive igneous rock)
igneous