metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (iron staining can cause the reddish-brown tint seen here); Luster: vitreous to dull; Crystal structure: Non-foliated, interlocking granoblastic texture; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (iron staining can cause the reddish-brown tint seen here); Luster: vitreous to dull; Crystal structure: Non-foliated, interlocking granoblastic texture; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure. The original quartz sand grains recrystallize and fuse together. It can be found in any geological age involving tectonic mountain building.
Uses & applications
Used heavily in construction as crushed stone for road ballast, floor coverings, and wall facing. Pure varieties are used to produce silica sand for glassmaking. Also popular as a durable kitchen countertop material.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is more resistant to weathering than the sandstone it originated from, which is why it often forms the jagged peaks of mountain ranges.
Field identification & locations
Identify in the field by its extreme hardness and the fact that it breaks across the grains, rather than around them (unlike sandstone). Commonly found in folded mountain belts like the Appalachians or the Alps. Collectors look for pieces with unique inclusions or desert varnish.
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