metamorphic
Quartzite
Quartzite (Primary mineral: SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow, tan, or brown iron staining; Luster: Vitreous (glassy) to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal or irregular fracture); Specific Gravity: 2.6 - 2.8.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous (glassy) to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow, tan, or brown iron staining; Luster: Vitreous (glassy) to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal or irregular fracture); Specific Gravity: 2.6 - 2.8.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together. This specimen appears to have formed in an environment with iron oxide infiltration, causing the yellowish rind.
Uses & applications
Used extensively in construction as road ballast, gravel, and building stone. Highly durable and resistant to chemical weathering. Higher purity specimens are used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often survives intense weathering better than the surrounding rocks, frequently forming the tops of ridges and mountains. It can be distinguished from sandstone because it breaks through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its superior hardness (it will easily scratch glass) and lack of reaction to acid. Often found in mountainous regions or ancient shield areas. Collectors should look for unique colors or embedded mineral inclusions.
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