mineral
Black tourmaline (schorl)
Schorl, NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄
AI-generated identification · may be incorrectTypically black with a vitreous to subvitreous luster and strong lengthwise striations; trigonal crystals, Mohs hardness 7–7.5, specific gravity about 3.2. The specimen appears to be a rough, elongated crystal fragment.
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Physical properties
Typically black with a vitreous to subvitreous luster and strong lengthwise striations; trigonal crystals, Mohs hardness 7–7.5, specific gravity about 3.2. The specimen appears to be a rough, elongated crystal fragment.
Formation & geological history
Forms in boron-rich granitic pegmatites and some metamorphic rocks as magma cools and hydrothermal fluids crystallize; deposits range from ancient to geologically recent.
Uses & applications
Used as a mineral specimen and, when transparent or well-formed, in jewelry; tourmaline is also valued by collectors.
Geological facts
Schorl is the most common tourmaline species, and its pronounced longitudinal grooves are a useful identifying feature.
Field identification & locations
Look for a black, prismatic crystal with parallel striations and a hardness sufficient to scratch glass; common sources include Brazil, Afghanistan, Pakistan, and the United States. The pictured form is consistent with schorl, though image-only identification is not definitive.
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Epidote
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Unidentified pink-and-gray mineral or rock specimen
Undetermined; the image is too blurry for reliable identification
mineral