What Are The Different Types of Rocks?

Rocks are a natural feature of the Earth’s surface, and their variety and features vary widely depending on their age, composition and formation. There are five major types of rocks – igneous, sedimentary, metamorphic, volcanogenic and sediment chutes. Each type of rock can be further divided into many different classifications, enabling researchers to precisely describe individual rock samples. In this article, we will discuss the major streams of rocks and what sets them apart.

Igneous Rocks

Igneous rocks are formed when molten or partially molten material, called magma or lava, cools and crystallizes into a solid. Magma forms when this molten material is released and forced up through the Earth’s crust, while lava results when magma reaches the surface through a volcanic eruption and cools rapidly. As this molten material cools, the interlocking mineral crystals form igneous rocks with a wide range of textures, from glassy and smooth to rough and coarse. The five main igneous rock types are basalt, gabbro, granite, rhyolite and obsidian.

Basalt

Basalt is the most common igneous rock type on Earth, and it is formed when molten rock cools relatively quickly in the presence of earth’s atmosphere. Basalt can be found on the ocean floor, in the form of vast stretches of seabed or in a single outcropping landmass such as Hawaii’s Big Island. Its relative abundance is due to its ability to crystalize quickly in many different environments. Basalt is also composed primarily of calcium-rich plutonic rocks, which are composed almost entirely of calcium-rich minerals such as feldspar and pyroxene, amongst others. Due to its high abundance, basalt is often used to add texture to architectural finishes, provide a base for landscaping projects and as an aggregate for road base.

Gabbro

Like basalt, gabbro is another common type of igneous rock formed when molten magma cools relatively quickly in the presence of Earth’s atmosphere. It is typically characterized by its coarse texture and dark coloration due to its high iron and magnesium mineral content. Gabbro’s most common purpose is as an aggregate material in road and runways construction or in landscaping applications. Gabbro is also often found in combination with other minerals, as is often seen in ophiolite sequences. Ophiolites are naturally occurring geological sections formed by the convergence of diverging crustal plates that form distinctive rock layers.

Granite

Granite is a coarse-grained igneous rock type composed of quartz, feldspar and muscovite mica crystals. It forms from magma that cools slowly beneath the Earth’s surface, forming large mineral grains with a lower silica content than other igneous rock types. Granite comes in many colors ranging from white to black to red, making it an attractive stone for construction applications like building façades, paving stone and even decorative countertops.

Rhyolite

Rhyolite rocks are mostly composed of quartz and feldspar with a much higher silica content than other types of igneous rocks such as granite and basalt. Rhyolitic magma is formed near the surface of the Earth when temperatures reach over 1000 degrees Celsius. It solidifies at very rapid speeds and typically produces extremely fine-grained crystalline rocks with tiny crystals visible to the naked eye. Rhyolite is sometimes used in sculpture or carved into decorative objects due to its unique coloration and texture.

Obsidian

Obsidian is an extremely fine-grained igneous rock produced from magma that cools quickly above the Earth’s surface before crystals have a chance to form. It is smooth to the touch, usually uniform in texture, jet-black in color, and contains very few inclusions or discolorations. Obsidian was prized by ancient civilizations for its sharp cutting properties. Blades made from it have been found in historic sites all over the world, including ancient Egypt and Native American artifacts from North America.

Sedimentary Rocks

Sedimentary rocks are made from wind-ground sediments or pieces eroded from pre-existing rocks that have been eroded by water or wind action over time. These pieces are deposited on a present-day landscape until they are buried in deeper layers of soil or sediment. Pressure and cementation cause these particles to solidify into sedimentary rocks often visible in the form of layers in walls or on cliffs. The most common sedimentary rocks are limestone, sandstone and shale, but there are many more varieties.

Limestone

Limestone is a sedimentary rock composed primarily of calcite or aragonite (minerals that form from dissolved calcium carbonate in marine environments). It is among the softest rock types, ranging from 0.5 up to 4 on the Mohs scale of hardness. As a result, limestone has been used throughout history for a wide range of applications such as building blocks for castles, countertops for kitchens and even agricultural lime for neutralizing soil acidity. Additionally, limestone has a wide range of colors from white to tan, making it a popular choice for decorative finishes and landscape projects.

Sandstone

Sandstone is a sedimentary rock composed mostly of quartz grains ranging in size from 0.1 millimeters to 2 millimeters in particle size. Sandstone’s composition varies drastically depending on where it’s sourced, so sandstone can be composed almost entirely of quartz with additional granite or shale material, or contain 1-15% clay material or iron oxide. It is classified as a medium-hard sedimentary rock with a hardness ranging from 6-7 on the Mohs scale. Sandstone is perhaps best known for its unique textures when polished which makes this type of rock ideal for decorative surfaces like floors and countertops..

Shale

Shale is composed predominantly of clastic sedimentary material – it’s composed mostly of clay flakes with little active quartz alongside silt, sand and other small pieces of mineral material. Shale ranges from 1-7 on the Mohs scale and can have shades ranging from yellowish gray to deep black depending on the type of plant matter that was mixed into it eons ago before it transformed into stone. Shale can be found all over the world but has been used most famously in construction applications like shingle roofs or landscaping materials such as edging–for driveways or pathways–due to its unique appearance when cut into thin slices.

Metamorphic Rocks

Metamorphic rocks are formed when existing rocks are changed by temperatures and pressure deep within the Earth’s crust or upper mantle layers. Common metamorphic rocks include slate, schist, marble and gneiss all with their own hardness rating on the Mohs scale from 1-10 with 10 representing the hardest types such as diamonds or quartzites.. These alterations can cause the improved physical qualities usually breaking more evenly than other siliceous minerals and giving them an angular appearance when compared to their preexisting counterparts.

Slate

Slate is a medium-hard metamorphic rock composed mainly of mica (muscovite) combined with various amounts of quartz, pyroxene and calcite mineral particles. Its texture can vary from massive (no layers) to foliated (layered) providing an intriguing appearance that makes it desirable for applications such as roofing slate tiles or pool decking. Its hardness can range anywhere from 2-6 on the Mohs scale so extreme care should be taken when handling slate especially if used as flooring tiles or counter slabs as part of home decorating projects as any sharp objects could scratch its surface easily by mistake.

Schist

Schist is another medium-hard metamorphic rock whose name derives from Greek words meaning “split” since its texture can vary depending on its composition – schist has distinct layered formations that usually appear after movement along tectonic plates has occurred in either direction giving the rock a split characteristic that increases its interest for decorative use on walls., stair treads or window frames in residential dwellings or commercial establishments. Schist ranges from 4-6 on the Mohs scale so strength wise it falls somewhere between slate and marble – not extreme enough like granites or steel/diamond but still comparably strong enough to bear heavier slabs/pieces when used for construction purposes like sidewalks or roadways..

Marble

Marble is a medium-hard metamorphic rock composed mainly of recrystallized calcite particles with various clastic sedimentary particles present as well – marble has a lustrous surface that makes it highly sought after in construction projects where smooth surfaces are desired such as floor tiles/slabs or window frames/arches/pillars in classic Greek/Roman architecture motifs.. Its hardness has been reported to range anywhere from 3-6 on the Mohs scale so proper care should be taken when handling both polished marble slabs/cuts as well as unfinished slabs/pieces that have yet to undergo their finishing process..

Gneiss

Gneiss is another hard metamorphic rock composed mainly of recrystallized granite minerals such as quartz & feldspars with varying amounts of mica flakes.. Its banded appearance gives it an interesting texture for applications such as flagstones for landscaping/gardening & decorative panels for construction projects – its texture can range anywhere from flat & linear to wavy & irregular depending on how fast/slow it was cooled during Metamorphism so properly cut & fit pieces should be chosen carefully when doing construction projects.. Gneiss typically ranges between 5-7 on de Mohs scale so strength wise it falls right between Marble & Granite types making it useful for both structural/construction purposes & decorative purposes when used correctly & correctly maintained..

Volcanic Rocks

Volcanic rocks are created through intense heat and pressure resulting from volcanic eruptions – they form around vent sites where magma has either erupted outwards & cooled upon contact with outside atmosphere or recoiled back downwards after contact & cooled before reaching Earth’s surface either way taking solid form upon cooling.. Common varieties include pumice & scoria whose hardness & composition vary greatly depending on composition & type – pumice typically ranges between 5-6 on Mohs scale making it only slightly harder than sandstones & claystones while Scoria ranges between 6-8 due to higher concentration of basaltic minerals present making it comparably harder than just basalts & gabbros alone..

Sediment Chutes

Sediment chutes are landforms created by accumulation of rock particles over an erosional feature – they form by material sliding down preferential channels along fault lines or other distinguishing landforms such as cliff faces leading them to collect at specific locations where they eventually fuse together & form distinct chute shapes.. Even though Sediment chutes can technically be part of any classification due to their complex formation process involving both transportative & erosive forces we define them separately here due its importance in geology & engineering – understanding where sediment chutes exist helps us map out potential disaster locations (Landslides specifically) as well as develop stronger approaches towards soil conservation which can help communities prevent further destruction during flash floods/heavy rains etc..

In conclusion, there are five major types of rocks – igneous, sedimentary, metamorphic, volcanogenic and sediment chutes – each with multiple varieties that can provide unique textures or properties useful for particular applications in design or engineering.

This article, courtesy Study.com Academy provides further details about each type.