Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Quartz sandstone is a clastic sedimentary rock characterized by a high proportion (typically >90%) of quartz grains. The grains are usually well-sorted and well-rounded, indicating a long history of transport and abrasion. The color can vary widely depending on the cementing material and minor impurities, ranging from white, gray, and yellow to red, brown, and even purple. The texture is granular, and individual sand grains are often visible to the naked eye or with a hand lens. The rock is generally hard and durable due to the hardness of quartz and the strength of the cement.
How to Identify
- Color
- Highly variable, often white, gray, tan, yellow, red, brown, or pink, depending on the cementing agent and trace minerals. Pure quartz sandstone is typically white or light gray.
- Luster
- Dull to vitreous (glassy) on individual quartz grains, overall earthy to granular.
- Texture
- Clastic, granular, with sand-sized grains (0.0625 mm to 2 mm) that are typically visible and feel gritty to the touch. Grains are often well-sorted and well-rounded.
- Crystal Form
- Individual quartz grains are anhedral to subhedral, often rounded. The rock itself does not exhibit a distinct crystal form.
- Cleavage
- No rock cleavage. Individual quartz grains lack cleavage but exhibit conchoidal fracture.
- Geological Environment
- Formed in high-energy sedimentary environments such as beaches, dunes (deserts), river channels, and shallow marine shelves where currents are strong enough to transport and sort sand-sized particles, and where chemical weathering has removed less stable minerals.
Key Facts
- Hardness: 7 (for individual quartz grains); overall rock hardness varies with cementation, but generally hard.
- Specific Gravity: 2.65 (for quartz); overall rock 2.2-2.8, depending on porosity and cement.
- Crystal System: Trigonal (for individual quartz crystals); rock is amorphous in terms of overall crystal system.
- Color: Highly variable, often white, gray, tan, yellow, red, brown, or pink.
- Luster: Dull to granular, individual grains vitreous.
- Transparency: Opaque to translucent (for the rock); individual quartz grains can be transparent to translucent.
- Fracture: Conchoidal (for individual quartz grains); overall rock fracture is irregular to granular.
- Cleavage: None (for quartz); rock has no cleavage.
- Composition: Predominantly SiO2 (quartz), typically >90%, with minor amounts of other minerals and cementing agents (silica, calcite, iron oxides, clay minerals).
Quick Check
- Color: Variable (white, gray, tan, red, brown)
- Luster: Dull to granular, individual grains vitreous
- Streak: White (due to quartz)
Physical Characteristics
- Crystal Habit: Anhedral to subhedral, rounded grains (for quartz).
- Cleavage Type: None.
- Fracture Type: Conchoidal (for quartz grains); irregular to granular (for the rock).
- Tenacity: Brittle.
- Luster Type: Vitreous (for quartz grains); dull to earthy (for the rock).
Formation
Quartz sandstone forms from the lithification of sand-sized grains (0.0625 mm to 2 mm) that are predominantly composed of quartz (SiO2). These grains are typically derived from the weathering and erosion of pre-existing rocks, transported by wind, water, or ice, and then deposited in various sedimentary environments such as beaches, rivers, deserts, and shallow marine settings. Over time, burial and compaction, along with cementation by minerals like silica (quartz overgrowths), calcite, or iron oxides, transform the loose sand into solid sandstone. The high quartz content indicates significant weathering and transport, leading to the removal of less stable minerals.
Usage
Quartz sandstone is a widely used construction material for building facades, paving, and dimension stone. It is also a significant source of silica for glass manufacturing, ceramics, and as an abrasive. High-purity quartz sandstone can be used in the production of silicon for semiconductors and solar panels. It also serves as an important reservoir rock for oil, natural gas, and groundwater due to its porosity and permeability.
Age Distribution
Found throughout the geological record, from Precambrian to Cenozoic.
Where to Find
Colorado Plateau, USA
Extensive formations like the Navajo Sandstone and Entrada Sandstone, known for their iconic red rock landscapes.
Appalachian Basin, USA
Numerous quartz sandstone units, including the Oriskany Sandstone, important for natural gas reservoirs.
Sahara Desert, North Africa
Vast ancient and modern dune fields contribute to extensive quartz sandstone deposits.
Australia
Significant quartz sandstone formations, such as those found in the Sydney Basin and parts of Western Australia.
Brazil
Extensive quartz sandstone deposits, particularly in the Paraná Basin.
Finding Tips
Look for Sedimentary Structures
Cross-bedding, ripple marks, and scour marks are common in sandstone and indicate depositional environments.
Examine Grain Characteristics
Use a hand lens to observe grain size, sorting, and rounding. Well-sorted, well-rounded quartz grains are indicative of mature quartz sandstone.
Test Hardness
Quartz grains are hard (Mohs 7). The rock as a whole will be hard, though the cement may be softer. It will scratch glass.
Check for Acid Reaction
If the cement is calcite, it will effervesce with dilute hydrochloric acid. Quartz itself will not react.
Similar Rocks
Arkose
Arkose
Also known as: Feldspathic Sandstone
Greywacke
Greywacke
Also known as: Dirty Sandstone
Siltstone
Siltstone
Also known as: Mudstone (fine-grained)
Scientific Classification
- Mineral Class
- Silicate (for quartz)
- Group
- Tectosilicate (for quartz)
- Crystal System
- Trigonal (for quartz)
- Chemical Formula
- SiO2 (for quartz)
- Composition
- Silicon dioxide (quartz) is the primary component, with varying amounts of cementing materials (e.g., silica, calcite, iron oxides) and trace accessory minerals.
Explore Quartz Sandstone
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.