metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with pink or red tints; Luster: vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, often with pink or red tints
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with pink or red tints; Luster: vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. High heat and pressure cause the individual sand grains to recrystallize and fuse together, creating an extremely durable rock. This sample likely originates from the Proterozoic or Paleozoic eras.
Uses & applications
Used widely in construction for railway ballast, floor tiles, and countertop surfaces. High-purity quartzite is also a source of silica for glassmaking and industrial abrasives.
Geological facts
Quartzite is so hard that when it breaks, the fracture line passes through the sand grains themselves rather than around them, which distinguishes it from sandstone. It is one of the most resistant rocks to weathering and often forms the tops of mountain ridges.
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 a fresh break. It is commonly found in fold mountain belts globally.
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