Sandstone is a clastic sedimentary rock. It is the most common sedimentary rock found in sedimentary basins worldwide. Sandstone is sand cemented together into a rock. A sandstone rock can be simply identified by simply looking at it. However, a closer examination reveals an interesting mix-up of sediment, cement, and matrix. Research into this rock often reveals useful geological information.
Sandstone can be composed of sand-size grains of minerals, other rocks, or organic materials. A mineral cement binds the sand grains together.
Sandstone reserves are formed by sand delivered to the basin by rivers, waves, or wind. The sediment can be organic or inorganic. An interesting fact about sandstone is that it is an integral part of all sedimentary rocks. Some sedimentary rocks may have up to 20-25% sandstone.
Sandstone can take various colors due to impurities in the rock, but it is usually brown, yellow, tan, red, gray, or black.
Sandstone is composed of sand-sizes (0.062 – 2 mm) silicate particles. The silicate can be quartz or feldspar. Both elements are highly resistant to weathering events on the earth’s surface. The sand grains are conveniently called framework grains.
Sandstones with more than 30% grains of gravel are classified as conglomerates or breccia. Both of these rocks are other common sedimentary rocks.
Rock formations made up of sandstone are highly porous, allowing water and fluid percolation. It makes valuable aquifers and petroleum reserves.
Sandstone changes into quartzite when it is exposed to regional metamorphism.
Some accessory minerals are also present in sandstone. The common accessory minerals include olivine, micas (muscovite and biotite), pyroxene, and corundum. Many of these minerals are denser than silicate minerals in the rock. The cement in sandstone is usually silica, calcium carbonate, or iron oxide. The cement may enter the matrix or fill the spaces where there is no matrix.
Some sandstone reserves may have fossils as well. However, its formation environments aren’t ideal for fossil preservation.
Sandstones usually contain matrix and cement besides sediment particles. The matrix includes fine-grained silt and clay. It is a part of the sediment along with the sand. In contrast, the matrix enters later and holds the rock together. Sandstones containing more matrix are called poorly sorted (wacky), and that with little matrix and cement are called arenite. Arenite is well-sorted and clean. Wacky has a dirty appearance.
Sandstone forms at sand burial sites. The usual sites are river deltas. However, desert dunes and beaches may also leave sandstone beds. The red rocks in the Grand Canyon National park in Arizona, US, are sedimentary rocks formed in a desert setting.
Sandstone formation occurs when deeply buried sand is exposed to pressure and slightly higher temperatures. This allows the minerals to deform or dissolve and start moving. The mineral grains become more tightly knit together, forcing the sediment to compact and squeeze. The cementing material moves into the rock at this time and holds the rock together. The rocks can get different colors at this time due to impurities. For example, the red color comes from iron oxides.
Sandstone-forming environments are divided into terrestrial and marine environments.
- Lakes & rivers
- Alluvial fans
- Glacial outwash
- Tidal flats
- Storm deposits
- Submarine channels
Where is Sandstone Found?
Sandstone is a common rock, and its reserves are located in almost every part of the world. The United States has 4 major sandstone reserves in New York, Virginal, Michigan, and Wisconsin. Large reserves are also located in Europe, Asia, and Australia. European reserves are the largest in the world. The leading sandstone producers in Europe are Switzerland, France, and Germany. South Africa produces 8 varieties, and Germany has up to 64 varieties.
Sandstone has been used in the construction industry for centuries. Sandstone extracted from Stafford County, Virginia (Aquia Creek Sandstone) has been used in Washington’s government buildings like the White House and many others.
Many universities in Australia are made from sandstone. These universities were built during the colonial era and had many buildings made from sandstone. All of these universities are named sandstone universities.
Sandstone’s resistance to weathering varies depending on its quality. However, it is frequently used as a building and paving material because it is easy to work with.
Historically, sandstone has been used to make temples, churches, and homes. It is also used as a source of underground water. Since sandstone is porous, it is often used as a water filter to remove debris and sediment from running water.