metamorphic
Quartzite
Quartzite (composed primarily of Quartz, SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellowish or reddish staining from iron oxides; Luster: vitreous to dull; Crystal structure: Non-foliated, granular texture; Cleavage: none, breaks with a conchoidal or irregular fracture.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellowish or reddish staining from iron oxides; Luster: vitreous to dull; Crystal structure: Non-foliated, granular texture; Cleavage: none, breaks with a conchoidal or irregular fracture.
Formation & geological history
Quartzite forms through the metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together. These rocks are found in mountain belts and areas of tectonic activity globally, spanning from the Precambrian to more recent eras.
Uses & applications
Used extensively in road construction (crushed stone), as railroad ballast, for heavy-duty floor tiles, kitchen countertops, and occasionally for lapidary work or inexpensive jewelry when it exhibits unique colors.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the capstones of mountain ranges and ridges because it resists erosion much better than surrounding rocks. It can be distinguished from sandstone because it breaks across the grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and lack of reaction to acid. It is commonly found in riverbeds as rounded cobbles or in massive outcrops in metamorphic terrains. Look for a sugary, crystalline appearance.
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