Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Quartzite is a non-foliated metamorphic rock composed almost entirely of quartz (SiO2). It is characterized by its exceptional hardness, resistance to weathering, and a typically granular, sugary texture. The interlocking nature of its quartz grains makes it extremely tough and durable. While pure quartzite is white or light gray, impurities can impart various colors, including pink, red, purple, yellow, green, or blue. It is distinguished from sandstone by its metamorphic texture, where the original sand grains are no longer discernible, and fractures typically cut across the grains rather than around them.
How to Identify
- Color
- Typically white to light gray, but can be pink, red, purple, yellow, green, or blue due to impurities (e.g., iron oxides for red/pink, chlorite for green).
- Luster
- Vitreous (glassy) to greasy on freshly broken surfaces.
- Texture
- Granular, sugary, or saccharoidal. The interlocking quartz grains are typically visible, but individual sand grains are not easily distinguished. Non-foliated.
- Crystal Form
- Anhedral, interlocking mosaic of quartz crystals.
- Cleavage
- No true cleavage; exhibits conchoidal fracture.
- Geological Environment
- Formed in regions of regional metamorphism associated with mountain building (orogenic belts) or in contact metamorphic aureoles around large igneous intrusions. Often found in ancient cratonic areas and mountain ranges.
Key Facts
- Hardness: 7 on the Mohs scale
- Specific Gravity: 2.65 g/cm³
- Crystal System: Trigonal (for individual quartz crystals)
- Color: White, gray, pink, red, purple, yellow, green, blue
- Luster: Vitreous to greasy
- Transparency: Translucent to opaque
- Fracture: Conchoidal to subconchoidal
- Cleavage: None (though individual quartz crystals may show poor rhombohedral parting)
- Composition: Primarily quartz (SiO2), typically >90%.
Quick Check
- Color: White to light gray, various colors with impurities
- Luster: Vitreous to greasy
- Streak: White
Physical Characteristics
- Crystal Habit: Anhedral, interlocking granular mosaic
- Cleavage Type: None
- Fracture Type: Conchoidal to subconchoidal
- Tenacity: Brittle, extremely tough
- Luster Type: Vitreous (glassy) to greasy
Formation
Quartzite forms from the metamorphism of quartz-rich sandstone. This process involves intense heat and pressure, typically associated with regional metamorphism during orogenic events (mountain building) or contact metamorphism near igneous intrusions. During metamorphism, the individual quartz grains recrystallize, along with the silica cement that bound them, to form an interlocking mosaic of quartz crystals. This recrystallization eliminates the original pore spaces and grain boundaries of the sandstone, resulting in a rock that is much harder and more durable than its protolith.
Usage
Due to its extreme hardness, durability, and resistance to weathering, quartzite is widely used in construction as dimension stone (e.g., flooring, countertops, wall cladding), crushed stone for road construction and railway ballast, and as an aggregate in concrete. High-purity quartzite is also used in the manufacturing of silica brick, ferrosilicon, silicon carbide, and as a flux in metallurgical processes. Its aesthetic appeal, particularly in various colors, makes it popular for decorative purposes.
Age Distribution
Precambrian to Cenozoic, depending on the protolith and metamorphic event.
Where to Find
Appalachian Mountains, USA
Extensive quartzite formations, particularly in the Blue Ridge and Valley and Ridge provinces, such as the Erwin Quartzite and Weverton Quartzite.
Baraboo Range, Wisconsin, USA
Famous for its Precambrian Baraboo Quartzite, known for its distinctive purple-red color.
Scotland
Significant quartzite occurrences, including the Cambrian-age Eriboll Quartzite in the Northwest Highlands.
Brazil
Known for high-quality quartzite deposits, often used as dimension stone.
India
Various regions possess significant quartzite resources, utilized for construction and industrial purposes.
Finding Tips
Look for outcrops in metamorphic terrains
Quartzite is a common rock in ancient mountain belts and areas that have undergone significant regional metamorphism.
Test for hardness
Quartzite is extremely hard (Mohs 7). It will scratch glass and steel easily. A hammer blow will typically produce a conchoidal fracture rather than breaking along grain boundaries.
Examine fresh breaks
Unlike sandstone, where grains tend to break apart, in quartzite, the fracture will cut through the quartz grains, creating a smooth, glassy surface.
Check for sugary texture
The interlocking quartz grains often give quartzite a distinctive sugary or saccharoidal texture, especially on weathered surfaces.
Similar Rocks
Sandstone
Sandstone
Also known as: Arenite
Chert
Chert
Also known as: Flint, Jasper, Agate
Novaculite
Novaculite
Also known as: Arkansas Stone
Scientific Classification
- Mineral Class
- Silicate (specifically Tectosilicate)
- Group
- Quartz Group
- Crystal System
- Trigonal (for constituent quartz)
- Chemical Formula
- SiO2
- Composition
- Silicon dioxide
Explore Quartzite
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.