metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be green, pink, or yellow due to mineral impurities; Luster: vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: none (breaks with conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
Identified More metamorphic →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be green, pink, or yellow due to mineral impurities; Luster: vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: none (breaks with conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, typically during regional metamorphism at convergent plate boundaries. The sand grains recrystallize and fuse together, creating an extremely durable rock. Geological age varies widely from Precambrian to Cenozoic.
Uses & applications
Used heavily in construction for road ballast, roofing granules, and as a decorative building stone. In its purest forms, it is used to produce silica sand for glassmaking and industrial abrasives. High-quality specimens are used in jewelry and lapidary art.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in mountain ranges, forming prominent ridges and peaks. Unlike sandstone, which breaks around the sand grains, quartzite breaks through the quartz grains because the matrix is just as strong as the grains themselves.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, 'sugary' texture. It lacks the fizzing reaction to acid seen in marble. Common in mountain belts and as rounded river stones/cobbles due to its resistance to erosion.
More like this
