metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or pink (this specimen shows reddish-brown staining); Luster: vitreous to dull; Crystal structure: trigonal (granular); Cleavage: none, breaks with a conchoidal or irregular fracture.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
Identified More metamorphic →
Explore Quartzite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or pink (this specimen shows reddish-brown staining); Luster: vitreous to dull; Crystal structure: trigonal (granular); Cleavage: none, breaks with a conchoidal or irregular fracture.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the individual quartz grains to recrystallize and fuse together into a dense, hard rock. This specimen appears to be a river-worn cobble, likely of Paleozoic or Precambrian age depending on the local geology.
Uses & applications
Used as a decorative stone in landscaping, a source of silica for glassmaking, in construction as crushed stone for road beds or railway ballast, and occasionally for high-end countertops.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the jagged peaks of mountain ranges because it resists weathering better than surrounding rocks. It can be distinguished from its parent sandstone because it breaks across the grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Look for a sugary, granular texture on fresh breaks. It is commonly found in ancient mountain belts or as rounded cobbles in riverbeds.
More like this
