mineral
Polished black stone, likely hematite
Hematite (Fe₂O₃), possibly magnetite or a hematite-rich ironstone
AI-generated identification · may be incorrectDark gray to black, highly polished metallic-to-submetallic luster, with smooth rounded shaping. Hematite has Mohs hardness 5–6.5, specific gravity about 5.0–5.3, and no prominent cleavage; a red-brown streak is diagnostic. The image alone cannot reliably distinguish it from magnetite or black glass.
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Physical properties
Dark gray to black, highly polished metallic-to-submetallic luster, with smooth rounded shaping. Hematite has Mohs hardness 5–6.5, specific gravity about 5.0–5.3, and no prominent cleavage; a red-brown streak is diagnostic. The image alone cannot reliably distinguish it from magnetite or black glass.
Formation & geological history
Hematite forms through oxidation of iron-bearing minerals, hydrothermal activity, sedimentary chemical precipitation, and metamorphism; deposits range from Precambrian banded iron formations to younger ore bodies. This specimen appears tumbled or polished.
Uses & applications
Used extensively as iron ore, pigment, and ornamental material; polished pieces are sold as beads, cabochons, and pocket stones. Common specimens typically have modest value.
Geological facts
Despite its black appearance, hematite commonly produces a reddish-brown streak on unglazed porcelain. Magnetite is strongly magnetic, whereas hematite is usually weakly magnetic or nonmagnetic.
Field identification & locations
Common localities include Brazil, Australia, South Africa, the United States, and India. Test streak, magnetism, and density; a glassy black appearance with no streak could indicate obsidian or manufactured glass instead.
