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 incorrect

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.

Identified September 26, 2026More metamorphic →

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Physical properties

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.