metamorphic
Weathered iron-stained quartzite or chert nodule
Siliceous rock composed chiefly of microcrystalline quartz (SiO₂), with iron-oxide staining and possible clay/minor carbonate minerals
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; cream, tan, reddish-brown, and gray colors; dull to waxy luster; massive, fine-grained texture with irregular fracture and no obvious cleavage. The porous cavities and rusty staining suggest strong weathering or partial replacement, so exact identification from the image is limited.
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Physical properties
Hardness about 6.5–7 Mohs; cream, tan, reddish-brown, and gray colors; dull to waxy luster; massive, fine-grained texture with irregular fracture and no obvious cleavage. The porous cavities and rusty staining suggest strong weathering or partial replacement, so exact identification from the image is limited.
Formation & geological history
Likely formed from silica-rich sediment that lithified and/or recrystallized, then acquired iron staining and surface cavities during weathering; its geological age cannot be determined visually. Similar material occurs in weathered sedimentary and metamorphic terrains worldwide.
Uses & applications
Usually a collector specimen, landscaping stone, or teaching sample; sound quartzite can be used as aggregate and building stone, but this irregular weathered piece has little commercial value.
Geological facts
The red-brown colors commonly come from hematite and goethite rather than the primary rock. A steel file should barely scratch it, while glass may be scratched by a fresh surface.
Field identification & locations
Look for a very hard silica-rich body, granular or waxy fracture, and rusty iron-oxide coatings; acid testing and a fresh broken surface help distinguish quartzite from chert, jasper, or weathered carbonate rock. Common in quartz-rich mountain belts and gravel deposits.
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