metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically grey, white, or tan with possible reddish stains from iron; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (fractures across grains); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically grey, white, or tan with possible reddish stains from iron; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (fractures across grains); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together, creating an extremely hard and durable rock. It can date back to any geological age where tectonic mountain building occurred.
Uses & applications
Used as a decorative stone in construction, road ballast, railway ballast, and ground up for glass manufacturing. It is also used for paving stones and wall coverings due to its durability.
Geological facts
Quartzite is so hard that it will scratch window glass and even steel. Unlike sandstone, which breaks around its grains, quartzite breaks right through the quartz grains because the bonds between them are as strong as the grains themselves.
Field identification & locations
Identify in the field by its sugary, crystalline texture and extreme hardness. It is commonly found in folded mountain belts globally, such as the Appalachians or the Alps. It lacks the fizz of limestone when exposed to acid.
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