metamorphic
Iron-stained quartz-rich rock, likely ferruginous quartzite
Quartzite (predominantly SiO₂) stained by iron oxides, likely hematite and goethite
AI-generated identification · may be incorrectOpaque, rusty orange-brown and cream, with a rough, granular texture and no obvious cleavage; quartz has Mohs hardness 7 and vitreous to dull luster. The photo does not show enough detail to confirm interlocking quartz grains, so identification is provisional.
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Physical properties
Opaque, rusty orange-brown and cream, with a rough, granular texture and no obvious cleavage; quartz has Mohs hardness 7 and vitreous to dull luster. The photo does not show enough detail to confirm interlocking quartz grains, so identification is provisional.
Formation & geological history
Quartz-rich sandstone recrystallized during metamorphism, with later iron-oxide staining or cementation; age cannot be determined from appearance alone.
Uses & applications
Quartzite is used as crushed aggregate, paving and building stone, and occasionally as decorative stone; this rough specimen is mainly of collector or educational interest.
Geological facts
Iron oxides commonly color otherwise pale quartz-rich rocks red, orange, or brown. Quartzite typically scratches glass and does not fizz in dilute acid.
Field identification & locations
The reported Rio de Janeiro area has varied igneous and metamorphic bedrock, so a quartz-rich, iron-stained rock is plausible regionally. Check for a very hard surface and grains that fracture through rather than around individual grains; a close-up or hardness test would improve identification.
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