metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron impurities often cause yellow, tan, or reddish-brown staining; Luster: vitreous to dull; Crystal structure: hexagonal (internal microcrystalline structure); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron impurities often cause yellow, tan, or reddish-brown staining; Luster: vitreous to dull; Crystal structure: hexagonal (internal microcrystalline structure); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz sand grains and silica cement to recrystallize into a dense, interlocking matrix. It is found in mountain belts and Precambrian shields worldwide.
Uses & applications
Used as crushed stone for road construction and railway ballast; in manufacturing glass and ceramics; as decorative dimension stone; and historically as a material for stone tools (lithics) due to its hardness.
Geological facts
Quartzite is so tough that it often outlasts surrounding rock types, forming the caps of ridges and mountains. Unlike sandstone, which breaks around its grains, quartzite breaks through the grains due to its high level of recrystallization.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its granular, sugary texture. It is often found in riverbeds as smooth, rounded cobbles or along mountain ridges. Collectors should look for unique coloration or banded patterns.
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