metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Pinkish-tan to light purple (stained by iron oxides); Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Pinkish-tan to light purple (stained by iron oxides)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pinkish-tan to light purple (stained by iron oxides); Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Over deep geological time, heat and pressure cause the individual quartz grains to recrystallize and fuse into a dense, hard rock. This specimen appears water-worn, likely from a river or glacial deposit.
Uses & applications
Used as a high-quality decorative stone, in construction as crushed stone for road beds, and as an abrasive. Certain pure varieties are used for glassmaking.
Geological facts
Quartzite is so hard that when it breaks, it breaks through the individual quartz grains rather than around them, which is a key distinction from sandstone. It is highly resistant to chemical weathering.
Field identification & locations
Identify in the field by its hardness (it will easily scratch glass) and its 'sugary' texture on a fresh break. Commonly found in mountainous regions or as rounded cobbles in stream beds.
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