metamorphic
Quartzite River Rock
Metaquartzite (majorly SiO2)
Hardness: 7 (Mohs scale); Color: light grey to tan; Luster: dull to vitreous; Crystal structure: non-foliated, granular; Cleavage: none; Specific gravity: approx. 2.65
- Hardness
- 7 (Mohs scale)
- Color
- light grey to tan
- Luster
- dull to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: light grey to tan; Luster: dull to vitreous; Crystal structure: non-foliated, granular; Cleavage: none; Specific gravity: approx. 2.65
Formation & geological history
Formed from the recrystallization of quartz-rich sandstone under intense heat and pressure (regional metamorphism). This specimen is a cobble smoothed by river or beach erosion.
Uses & applications
Used in construction as crushed stone or gravel, in landscaping for decoration, and historically for making stone tools due to its hardness and conchoidal fracture.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the crests of mountain ridges; it is much harder than the sandstone it originated from.
Field identification & locations
Identify in the field by its hardness (will easily scratch glass) and lack of reaction to acid. Commonly found in riverbeds, glacial deposits, and mountain outcrops. Look for a sugary, crystalline texture when broken.
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