mineral

Iron-Stained Quartz (Riverside Cobble)

Silicon Dioxide (SiO2) with Limonite/Hematite inclusions

Hardness: 7 (Mohs scale), Color: Translucent white to tan with patches of yellow/orange/brown staining, Luster: Vitreous to greasy, Crystal Structure: Hexagonal (trigonal), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Identified March 19, 2026More mineral →

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Physical properties

Formation & geological history

Formed in hydrothermal veins or as a major constituent of igneous rocks. The specimen shown is likely a water-worn cobble from a riverbed or alluvial deposit where it underwent physical weathering and chemical staining from iron oxides over thousands of years.

Uses & applications

Common industrial use includes glass manufacturing and abrasives. In this specific cobble form, it is primarily used for decorative landscaping, lapidary tumbling, or as a beginner's mineral collection specimen.

Geological facts

Quartz is the second most abundant mineral in Earth's continental crust. The yellow-orange 'skin' on this rock is known as a 'desert varnish' or iron staining, which occurs when iron minerals in water or soil oxidize on the surface of the quartz.

Field identification & locations

Identify by its ability to scratch glass (high hardness), lack of cleavage, and waxy luster when wet. It is commonly found in riverbanks, glacial tills, and mountainous regions worldwide. For collectors, these are often sliced to reveal the inner purity versus the outer weathering.

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