Quartz Sandstone

Sedimentary Rock

Quartz sandstone

Also known as: Arenite, Quartz Arenite, Orthoquartzite (when highly cemented)

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Description

Quartz sandstone is a clastic sedimentary rock composed of more than 90% quartz grains. It is typically light-colored, ranging from white, gray, and tan to yellow, brown, or reddish, depending on the cementing agent and minor impurities. The grains are usually well-sorted and well-rounded, indicating significant transport and abrasion. The texture can range from fine-grained to coarse-grained. The primary mineral, quartz, is highly resistant to chemical and physical weathering, making quartz sandstone a very durable rock. The porosity and permeability of quartz sandstone vary significantly depending on the degree of cementation and sorting of the grains.

How to Identify

Color: Typically light-colored: white, gray, tan, yellow, brown, or reddish. Color variations are often due to minor impurities or cementing agents (e.g., iron oxides for red/brown hues).
Luster: Dull to vitreous (glassy) on freshly broken surfaces, depending on the degree of cementation and the luster of individual quartz grains.
Texture: Clastic, granular, with sand-sized grains (0.0625 mm to 2 mm). Grains are often well-sorted and well-rounded in mature quartz sandstones. Can feel gritty to the touch.
Crystal Form: Individual quartz grains are typically anhedral to subhedral, often rounded due to transport. In highly cemented varieties, quartz overgrowths can create euhedral crystal faces within the pore spaces.
Cleavage: No rock cleavage. Individual quartz grains exhibit poor to indistinct cleavage (rhombohedral), but this is rarely observed in hand samples of sandstone.
Geological Environment: Forms in high-energy sedimentary environments where clastic sediments are transported and deposited, such as beaches, dunes (deserts), river channels, deltas, and shallow marine shelves. These environments promote the removal of unstable minerals and fine-grained matrix, leading to a high concentration of resistant quartz grains.

Key Facts

Hardness: Individual quartz grains are 7 on Mohs scale; the rock's overall hardness depends on cementation, typically 6-7 for well-cemented varieties.
Specific Gravity: 2.65 - 2.70 (for pure quartz grains; the rock's bulk specific gravity can vary with porosity and cement type, typically 2.2 - 2.6).
Crystal System: Trigonal (for individual quartz grains). The rock itself is an aggregate of grains.
Color: White, gray, tan, yellow, brown, reddish.
Luster: Dull to vitreous.
Transparency: Opaque to translucent (for the rock; individual quartz grains can be transparent).
Fracture: Conchoidal (for individual quartz grains); irregular to granular for the rock.
Cleavage: None (for the rock); individual quartz grains have poor/indistinct rhombohedral cleavage.
Composition: Predominantly quartz (SiO2), typically >90%. Minor constituents may include feldspar, mica, heavy minerals, and various cementing agents (silica, calcite, iron oxides, clay minerals).

Quick Check

Color: White, gray, tan, yellow, brown, reddish
Luster: Dull to vitreous (on grains)
Streak: White

Physical Characteristics

Crystal Habit: Anhedral to subhedral, often rounded grains of quartz.
Cleavage Type: Not applicable for the rock; individual quartz grains exhibit poor/indistinct rhombohedral cleavage.
Fracture Type: Irregular to granular for the rock; conchoidal for individual quartz grains.
Tenacity: Brittle.
Luster Type: Dull to vitreous.

Formation

Quartz sandstone forms from the lithification of sand-sized grains (0.0625 mm to 2 mm in diameter) that are predominantly composed of quartz (SiO2). These sand grains are typically derived from the weathering and erosion of pre-existing igneous, metamorphic, or older sedimentary rocks. The grains are transported by wind, water, or ice and deposited in various sedimentary environments such as beaches, rivers, deserts, and shallow marine settings. Over time, burial and compaction reduce porosity, and cementation by minerals like silica (quartz overgrowths), calcite, iron oxides, or clay minerals binds the grains together, forming sandstone. High maturity quartz sandstones, or quartz arenites, indicate extensive weathering, transport, and sorting, leading to a high percentage of stable quartz grains and a low percentage of unstable minerals and matrix.

Usage

Quartz sandstone has a wide range of uses due to its durability, abundance, and aesthetic qualities. Historically, it has been a primary building material for structures, monuments, and paving. It is used as an aggregate in concrete and asphalt, as a source of silica for glass manufacturing (especially high-purity quartz sandstone), in foundry molds, as abrasive material, and in hydraulic fracturing (proppant). Certain varieties are used as dimension stone for architectural applications, and some highly porous and permeable quartz sandstones serve as important reservoirs for oil, natural gas, and groundwater.

Age Distribution

Found throughout the geological record, from Precambrian to Cenozoic.

Where to Find

United States

Extensive deposits are found in the Appalachian Basin (e.g., Oriskany Sandstone), the Michigan Basin, the Illinois Basin, and throughout the Western US (e.g., Navajo Sandstone, St. Peter Sandstone). Significant occurrences in states like Wisconsin, Illinois, Pennsylvania, and Utah.

Canada

Found in various sedimentary basins, including the Western Canada Sedimentary Basin and parts of the Canadian Shield.

Australia

Widespread in many sedimentary basins, including the Sydney Basin and parts of Western Australia.

United Kingdom

Notable occurrences in the Permian and Triassic sandstones of England (e.g., Penrith Sandstone) and Carboniferous sandstones in Scotland and Wales.

Middle East

Important reservoir rocks in many oil-producing regions, particularly in Saudi Arabia, Kuwait, and Iraq.

Brazil

Significant deposits in various basins, including the Paraná Basin.

Finding Tips

Look for Sedimentary Layers

Quartz sandstone typically occurs in distinct, often well-bedded, sedimentary layers or formations. Look for outcrops in road cuts, river banks, quarries, and coastal cliffs.

Examine Grain Composition

Use a hand lens to observe the individual grains. Quartz grains are typically clear to milky white, hard (scratches glass), and lack cleavage. A high proportion of these grains (over 90%) indicates quartz sandstone.

Assess Grain Shape and Sorting

Well-rounded and well-sorted grains are characteristic of mature quartz sandstones, indicating significant transport and reworking. This can be observed with a hand lens.

Check for Gritty Texture

Rub a sample between your fingers; it should feel gritty due to the sand-sized quartz grains.

Consider Color and Cement

While often light-colored, variations exist. Note the color and try to identify the cementing agent if possible (e.g., reddish for iron oxide cement, white for silica or calcite cement).

Similar Rocks

Arkose

Also known as: Feldspathic Sandstone

Greywacke

Also known as: Dirty Sandstone

Siltstone

Also known as: Silty Rock

Quartzite

Also known as: Metamorphosed Sandstone

Scientific Classification

Mineral Class: Silicate (for quartz)
Group: Clastic Sedimentary Rock
Crystal System: Trigonal (for quartz)
Chemical Formula: SiO2 (for quartz, the dominant mineral)
Composition: Primarily silicon dioxide (SiO2) in the form of quartz grains, with minor amounts of other minerals and cementing agents.

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