metamorphic
Red Quartzite (Stream-rounded Cobble)
Meta-quartzite (SiO2 with Hematite impurities)
Hardness: 7 (Mohs scale); Color: Reddish-brown to maroon; Luster: Vitreous to dull/waxy; Structure: Granofelsic; Cleavage: None (conchoidal fracture); SG: ~2.65
- Hardness
- 7 (Mohs scale)
- Color
- Reddish-brown to maroon
- Luster
- Vitreous to dull/waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Reddish-brown to maroon; Luster: Vitreous to dull/waxy; Structure: Granofelsic; Cleavage: None (conchoidal fracture); SG: ~2.65
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure caused individual sand grains to recrystallize into a dense, interlocking mosaic of quartz crystals. Often found as rounded cobbles due to fluvial (river) erosion.
Uses & applications
Used primarily as decorative landscaping stone, road ballast, and in some cases as abrasive material. High-quality smooth specimens are often used in lapidary for polishing or as worry stones.
Geological facts
Quartzite is so tough that it usually breaks through the original sand grains rather than around them. The red color is typically caused by minute inclusions of iron oxide (hematite) during the deposition of the original sandstone or the metamorphic process.
Field identification & locations
Identify in the field by its hardness (it will easily scratch glass) and lack of reaction to acid. Often found in glacial till or riverbeds. Smooth, rounded shapes like this specimen indicate significant transport by water or ice.
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