mineral
Raw botryoidal goethite/limonite specimen
Goethite (α-FeO(OH)), commonly mixed with limonite (hydrated iron oxides)
AI-generated identification · may be incorrectDark brown-black, earthy to submetallic luster with irregular botryoidal surfaces; typically opaque, hardness about 5–5.5 Mohs, and specific gravity roughly 3.3–4.3. The apparent blue-gray reflective patches may be wet surfaces or associated sulfide/mineral material; exact identification requires testing.
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Physical properties
Dark brown-black, earthy to submetallic luster with irregular botryoidal surfaces; typically opaque, hardness about 5–5.5 Mohs, and specific gravity roughly 3.3–4.3. The apparent blue-gray reflective patches may be wet surfaces or associated sulfide/mineral material; exact identification requires testing.
Formation & geological history
Forms as a secondary weathering and oxidation product of iron-bearing minerals, commonly in iron-ore deposits, hydrothermal veins, and soil environments; generally young to geologically ancient depending on host deposit.
Uses & applications
Used as an iron ore and historically as a brown-yellow pigment; attractive botryoidal pieces are collected, though this rough fragment has limited gem or commercial value.
Geological facts
Goethite commonly develops concentric, grape-like (botryoidal) coatings and may occur with hematite, quartz, pyrite, or manganese oxides. Limonite is a field term for mixtures of hydrated iron oxides rather than a single precisely defined mineral.
Field identification & locations
Identify by heavy feel, brown-yellow streak, opaque botryoidal crust, and lack of true glassy cleavage; a streak test and magnet test help distinguish it from sulfides. Common worldwide, especially in oxidized ore zones and iron-rich soils.
