metamorphic
Quartzite River Rock (with Limonite staining)
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, orange-brown (due to iron oxide coating), white internally; Luster: Dull/waxy exterior, vitreous interface; Structure: Granular, non-foliated; Cleavage: None (conchoidal fracture); SG: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- Dull/waxy exterior, vitreous interface
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, orange-brown (due to iron oxide coating), white internally; Luster: Dull/waxy exterior, vitreous interface; Structure: Granular, non-foliated; Cleavage: None (conchoidal fracture); SG: 2.6-2.7.
Formation & geological history
Originally formed as sandstone (sedimentary) and later subjected to intense heat and pressure (metamorphism) which fused quartz grains together. This specific specimen shows rounding from water erosion in a high-energy environment like a riverbed.
Uses & applications
Used as crushed stone for road construction, railway ballast, and decorative landscaping. High-purity quartzite is also used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in weathering processes, resulting in the rounded 'cobbles' often found in glacial till and stream beds. The orange color on this piece is 'desert varnish' or limonite staining from iron minerals.
Field identification & locations
Identify by its ability to easily scratch glass and its lack of reaction to acid. Look for a sugary texture on broken surfaces. Very common in riverbeds across North America and Europe.
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