mineral
Brown botryoidal mineral specimen, likely goethite/limonite
Goethite (α-FeO(OH)), possibly mixed with limonite (hydrated iron oxides)
AI-generated identification · may be incorrectDark brown to nearly black, earthy-to-submetallic luster with rounded botryoidal surfaces; hardness about 5–5.5 for goethite, specific gravity roughly 3.3–4.3. Crystal structure is orthorhombic, though specimens commonly appear massive or botryoidal.
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Physical properties
Dark brown to nearly black, earthy-to-submetallic luster with rounded botryoidal surfaces; hardness about 5–5.5 for goethite, specific gravity roughly 3.3–4.3. Crystal structure is orthorhombic, though specimens commonly appear massive or botryoidal.
Formation & geological history
Forms by oxidation and weathering of iron-bearing minerals, commonly in iron-rich hydrothermal veins, caves, soils, and gossans. Formation age depends on the deposit and may range from ancient to recent weathering.
Uses & applications
Used as an iron ore and historically as a brown/yellow pigment; attractive botryoidal pieces are collected but are generally inexpensive.
Geological facts
Goethite commonly produces yellow-brown streak and may occur with hematite, quartz, or manganese oxides. The image’s low resolution prevents secure separation from hematite or other dark iron-oxide minerals.
Field identification & locations
Field identification: test streak on unglazed porcelain—goethite/limonite gives yellow-brown, while hematite gives red-brown; it is also relatively heavy and nonmetallic. Common worldwide, especially in oxidized ore deposits and lateritic soils.
