metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: white to light gray; Luster: vitreous to dull; Crystal Structure: non-foliated grains; Cleavage: none; Specific Gravity: 2.6-2.7. It is extremely durable and breaks across grains rather than around them.
- Hardness
- 7 on Mohs scale
- Color
- white to light gray
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: white to light gray; Luster: vitreous to dull; Crystal Structure: non-foliated grains; Cleavage: none; Specific Gravity: 2.6-2.7. It is extremely durable and breaks across grains rather than around them.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. These deposits can range from Precambrian to much younger geological ages depending on the local tectonic history.
Uses & applications
Used extensively in road construction (as crushed stone), as railway ballast, and in the manufacturing of glass and ceramics. Polished varieties are used for kitchen countertops, flooring, and decorative carvings.
Geological facts
Quartzite is so tough that it often forms the crests of ridges and mountains because it resists weathering better than the surrounding rocks. Because it is nearly pure silica, it is also a primary source of silicon for electronic applications.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel blade) and its sugary, granular texture. It will not react with acid, unlike marble. Crystals are often visible as tiny sparkling points on fresh surfaces. Found worldwide in mountain belts.
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