mineral

Quartz geode with iron-oxide matrix

Quartz (SiO₂), likely with limonite/goethite and possibly calcite

AI-generated identification · may be incorrect

White to colorless, glassy crystals lining a cavity; quartz hardness 7, vitreous luster, hexagonal crystal system, and no cleavage. The rusty brown coating is iron oxide/hydroxide; some blockier crystals may be calcite, which is softer (Mohs 3) and rhombohedral.

Identified August 13, 2026More mineral →

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Physical properties

Formation & geological history

Formed when silica-rich groundwater deposited crystals inside a cavity or fracture, with later oxidation producing the brown iron-rich matrix. Exact age and locality cannot be determined from the image; such specimens commonly form in volcanic cavities or mineralized sedimentary fractures.

Uses & applications

Collected as a display specimen and sometimes sold as a small decorative geode; quartz is widely used in glass, electronics, abrasives, and engineered stone. This rough specimen has limited industrial significance.

Geological facts

The crystal-lined cavity is a vug or geode-like structure. A streak test, hardness test, and dilute acid test can distinguish quartz from calcite, though testing may damage the specimen.

Field identification & locations

Look for transparent vitreous crystals, hexagonal points, and rusty limonite/goethite; common sources include Brazil, Morocco, Mexico, and the United States. Avoid assuming locality from appearance alone.