metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, can be yellow or green; Luster: vitreous to grainy; Crystal structure: trigonal (recrystallized quartz grains); Cleavage: none; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, can be yellow or green
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, can be yellow or green; Luster: vitreous to grainy; Crystal structure: trigonal (recrystallized quartz grains); Cleavage: none; Specific gravity: 2.6-2.7.
Formation & geological history
Quartzite is a non-foliated metamorphic rock that forms from the metamorphism of pure quartz sandstone. It is created through high heat and pressure during regional metamorphism related to tectonic plate compression. It can form in any geological age, notably in Precambrian shields.
Uses & applications
Used as a crushed stone in road construction and railway ballast. Due to its durability, it is popular for kitchen countertops, floor tiles, and decorative stone. Sometimes used in glass making if remarkably pure.
Geological facts
Unlike sandstone, which breaks around the sand grains, quartzite is so strongly fused that it fractures through the quartz grains themselves. This makes it one of the most physically durable and chemically resistant rocks on Earth's surface.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife (hardness 7) and its sugary, crystalline texture that sparkles in the sun. Commonly found in folded mountain ranges. Collectors look for pieces with unique colors or translucent qualities.
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