metamorphic
Quartzite (River Pebble)
Metamorphic Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, reddish-brown (from iron staining), and beige; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture; Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Tan, reddish-brown (from iron staining), and beige
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, reddish-brown (from iron staining), and beige; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture; Specific gravity: 2.65
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, causing the original quartz grains to recrystallize. This specific specimen has been further shaped by fluvial (river) erosion, creating the smooth pebble texture.
Uses & applications
Used as decorative landscaping stones, raw material for glass manufacturing, high-quality railroad ballast, and occasionally for lapidary work like rock tumbling.
Geological facts
Quartzite is so durable that it can survive long periods of weathering. It is often much harder than the parent sandstone it originated from, and in the field, it will break through the quartz grains rather than around them.
Field identification & locations
Identify by its hardness (it will easily scratch glass) and its smooth, rounded appearance if found near water. It lacks the visible grains or 'sandiness' of sandstone. Found globally in riverbeds, glacial deposits, and mountain ranges.
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