metamorphic
Quartzite (Iron-stained)
Metamorphic Quartzite (primarily SiO2) with Limonite/Hematite staining
Hardness: 7 on Mohs scale. Color: Tan, orange, and reddish-brown due to iron oxide staining. Luster: Vitreous to greasy. Crystal structure: Granular, interlocking quartz grains. Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Tan, orange, and reddish-brown due to iron oxide staining
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on Mohs scale. Color: Tan, orange, and reddish-brown due to iron oxide staining. Luster: Vitreous to greasy. Crystal structure: Granular, interlocking quartz grains. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, usually during mountain-building events (orogeny). This specific river-worn cobble has been chemically weathered, allowing iron-rich water to stain the surface and grain boundaries.
Uses & applications
Commonly used as crushed stone for road construction, railway ballast, and as a decorative landscaping stone. In its purest forms, it is used to produce glass and industrial silicon.
Geological facts
Quartzite is so tough that it often resists weathering better than the rocks surrounding it, leading it to form the caps of ridges and mountains. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify in the field by its sugary, granular appearance and its extreme hardness; it cannot be scratched by a steel blade. This specimen shows characteristic rounding from being transported in a river or stream.
