metamorphic
Red Quartzite / River Siltstone
Quartzite (SiO2 with iron oxide inclusions)
Hardness: 6.5-7 (Mohs); Color: Reddish-brown to pink due to hematite pigment; Luster: Waxy to vitreous when polished; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Reddish-brown to pink due to hematite pigment
- Luster
- Waxy to vitreous when polished
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Reddish-brown to pink due to hematite pigment; Luster: Waxy to vitreous when polished; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to deep burial or tectonic activity recrystallize the sand grains into a dense, interlocking mosaic of quartz. This specific rounded shape is the result of fluvial erosion in a river bed.
Uses & applications
Used primarily as decorative landscaping stone, in aquarium decor, as a tumbling medium for rock polishers, or as a pocket stone for collectors. In large scale, quartzite is used for railway ballast and construction.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges it was part of, ending up as rounded pebbles in younger river systems. The red color suggests the presence of iron oxide during the original deposition of the parent sandstone.
Field identification & locations
Identify in the field by its hardness (it will scratch glass easily) and its granular, sugary texture on a fresh break. Common in glacial till or ancient river terraces. This specimen is a 'river rock' variety, smoothed by natural water action.
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