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Rock Definition

A rock is a naturally occurring material made up of hard crystals of various minerals. Rock gives the planet a sturdy structure. The crust of the Earth and the majority of its interior are made of rocks. Natural rock formation occurs when micro grains of various minerals are compressed by external pressure. The grains' size, arrangement, and shape form the texture of rock. Rocks and minerals are used in various products, such as cosmetics, automobiles, construction, and appliances.

Rock Definition

Types of Rock

Rock is the naturally produced solid mass or a combination of minerals or mineraloid materials. It is divided into groups based on the minerals present in it. In nature, there are numerous types of rocks, and the three main types of rocks are:

  1. Metamorphic Rocks
  2. Sedimentary Rocks
  3. Igneous Rocks

1. Igneous Rocks

Rock Definition

Igneous rocks are generated when magma or lava cools down and solidifies. These rocks are probably created during volcanic explosions. Its examples are diabase, diorite, gabbro, granite, pegmatite, and peridotite.

Types of igneous rock texture:

  1. Aphanitic rock has tiny grains that are invisible to the naked eye.
  2. Phaneritic rock has visible coarse-grained crystals.
  3. Pegmatitic rock has visible and very coarse-grained crystals.
  4. Porphyritic rock is made from large and fine-grained crystals.
  5. Vesicular rocks contain vesicles, and it is like a sponge (e.g., scoria and pumice).
  6. Pyroclastic rock is made up of angular grains that are released during the eruption.
  7. Glassy rock forms when lava cools quickly.

Types of igneous rocks:

1. Intrusive igneous rocks

Intrusive igneous rocks crystallize below the Earth's surface. Its examples include pegmatite, granite, and diorite.

2. Extrusive igneous rock

Extrusive igneous rock, commonly called volcanic rock, is created when molten lava cools on the surface of the Earth. Its examples include basalt, tuff, and pumice.

Examples of igneous rocks with characteristics

Rock Name Color Texture
1. Diorite Medium colored Course
2. Rhyolite Light-colored (pastel) Pastel
3. Obsidian Dark colored Glass
4. Tuff Fine-grained ash Ash particles

2. Sedimentary rocks

Rock Definition

Sedimentary rocks are formed when minerals and rock fragments settle out of water or air. It is formed by accumulating and solidifying biological waste, such as leaves, roots, and other plant waste. Common sedimentary rocks include limestone, clay, sandstone, chalk, and shale.

Types of sedimentary rocks:

1. Organic sedimentary rocks

Accumulation and solidification of organic residues, such as leaves, roots, and other plant or animal material, formed the organic sedimentary rocks.

2. Clastic sedimentary rocks

Clastic sedimentary rocks are generated from mechanical weathering waste.

3. Chemical sedimentary rocks

Chemical sedimentary rocks form when water moves through rock and dissolves some minerals. E.g., chert, limestone, banded iron formation, and evaporites.

Sedimentary rock applications:

  1. Cement is produced using limestone.
  2. Sedimentary rocks are utilized to construct earthen dams, railroad ballast, canals, and rock-fill dams.
  3. The materials utilized to build structural walls include sandstone and limestone.
  4. Rock gypsum is utilized to make plaster.
  5. Shale is utilized to produce cement.
  6. The thick-bedded, well-cemented, siliceous sandstone is used to construct tunnels.
  7. Re-crystallized marble is used to decorate building interiors, and it is also utilized for tabletop surfaces and statuary.
  8. Shale can be used as a filler in various paints.
  9. Wallboard is made from gypsum.

3. Metamorphic Rocks

Rock Definition

Metamorphic rocks are formed when existing rocks undergo a physical or chemical change at a high temperature. Metamorphic rocks can originate from igneous, sedimentary, or existing metamorphic rocks. New minerals that develop during metamorphism differ from the original minerals in size, shape, and orientation.

Types of metamorphic rocks:

1. Foliated metamorphic rocks

Foliation is the term used to describe a metamorphic rock with strata of aligned minerals. Foliated rocks form a platy or sheet-like structure that indicates the direction of pressure. Foliated metamorphic rocks include phyllite and gneiss. The rock is organized in layers & looks like stripes. The layers in rock generate under high pressure.

Examples of foliated metamorphic rock

Foliated Rock Characteristics
1. Schist A rock with large grains. It has huge crystals that are visible to the naked eye.
2. Slate Tough rock and has fine grains.
3. Gneiss A rock with large grains. Has irregular bands. These bands come in a variety of colors.

2. Non-foliated rocks

Non-foliated rocks do not have layered or banded appearances. Examples of non-foliated rocks are hornfels, marble, skarn, quartzite, and novaculite.

Applications of metamorphic rock:

  1. Metamorphic rocks are utilized to construct statues, structures, and monuments.
  2. Metamorphic gneiss is a useful building material that can be used for various purposes, including flooring, decorative stones, gravestones, building facing, and work surfaces.
  3. Schist is used in sculpting, paving, and garden decoration.
  4. Marble can be crushed and used in cleaning solutions and soaps.
  5. Slate is an excellent roofing material, and it is utilized as snooker tables, ornamental garden stones, and a writing surface in victorian classrooms.

The Transformation of Sedimentary into Metamorphic Rock

  1. Conglomerate transforms into gneiss and schist
  2. Limestone changes to schist and Crystalline limestone
  3. Shale transition from slate and schist
  4. Sandstone transforms into quartzite and gneiss

The Transformation of Igneous into Metamorphic Rock

  1. Granite changes to gneiss.
  2. Pyroxenite transforms into serpentine.
  3. Syenite becomes gneiss.
  4. Peridotite transforms into serpentine.
  5. Rhyolite and porphyry become schist.
  6. Diorite transforms into gneiss.
  7. Basalt transforms into schist.

Commonly Used Building Rocks

The most frequently used building rocks include marble, quartzite, granite, serpentine, limestone, chalk, sandstone, caliche, basalt and trap, slate, laterite, and gneiss.

1. Granite

Granite is an igneous rock created when magma solidifies at a significant depth below the Earth's surface. It is durable and hard. Granite's color depends on the quantity of feldspar present in it. It is easily polishable. Large engineering projects like the construction of a bridge, dams, and offshore structures utilize granite as a building material. It is also utilized to build walls, floors, staircases, and other structures.

2. Basalt and trap

Basalt and trap are utilized as pavement material, cement aggregate, railroad ballast, etc. Basalt and trap of red and yellow color are utilized to create an architectural ornament.

3. Syenite

Syenite has a coarse-grained structure, and its crushing strength ranges from 90 to 150 MPa. Although it comes in a variety of colors, most of them are light. Crushed syenite is regularly utilized to produce concrete. It is also utilized in the construction of exterior building walls.

4. Limestone

The accumulation of weathering particles forms limestone. It has significant amounts of calcium carbonate. Limestone is utilized to make cement and lime. It is also utilized for roofing, flooring, etc.

5. Chalk

A sedimentary rock called chalk contains only pure lime. It is highly lightweight and easily turned into powder. It is utilized to make lime putty.

6. Sandstone

Sandstone contains various minerals, including quartz, feldspar, and silica. It is used to construct columns, ornamental carvings, roofing, paving, and other structures.

7. Caliche

Caliche is commonly known as kankar. In the construction of pavements, kankar is utilized as aggregate. It's utilized to make hydraulic lime.

8. Marble

Marble is generated when limestone is exposed to extreme heat and pressure. Marble is a hard material. It comes in various colors and is polishable. Marble is utilized for steps, flooring, etc. As it's simple to carve into the desired shape, it is utilized in decorative and ornamental works on structures.

9. Slate

Slate has a foliated texture and is black. Slate is used for floors, roofs, walls, damp-proofing courses, etc.

10. Quartzite

Quartzite is utilized as cement and road aggregate. It is utilized to construct retaining walls, rubble masonry, stone pitching, etc.

11. Laterite

The structure of laterite is porous and spongy. Due to its softness and workability, laterite can be easily quarried. Moorum is produced when laterite breaks down, frequently used in road construction. Laterite is utilized in the construction of pavements and masonry.

12. Gneiss

Gneiss is another metamorphic rock created due to the transformation of granite. It has a foliated structure. Crushed gneiss is used for making pavement, building rough stones, pitching stones, etc.

Rocks in India

1. Rocks of the archaean system

It was formed during the pre-Cambrian era when the Earth's crust's top layer cooled and solidified. These rocks contain metallic and non-metallic minerals, including mica, asbestos, graphite, lead, zinc, gold, silver, tungsten, copper, manganese, and bauxite.

2. Rocks of dharwar system

It was formed as a consequence of the transformation of Archean rock sediments. These rocks can be found in Karnataka, Andhra Pradesh, Tamil Nadu, the Himalayas, Delhi, Madhya Pradesh, Orissa, Aravallis, and some regions of Jharkhand and Rajasthan. These rocks hold significant economic value. These rocks contain all notable metallic minerals such as iron, gold, manganese, etc.

3. Rocks of cuddapah system

It was formed due to the erosion and accumulation of Archean and Aharwar rocks, which took place between 140 and 600 million years ago. These rocks contain minerals like cobalt, manganese, copper, iron, nickel, etc.

4. Rocks of the vindhyan system

It was formed by the deposition of sand in river valleys & shallow ocean sediment.

5. Rocks of the tertiary system

It was formed between the Eocene and Pliocene eras. The rocks of the tertiary system can be found in Kashmir, the Great Plains' Bhangar, and Khadar.

Difference Between Rock and Stone

Stone Rock
1. Stone is a form of non-metallic mineral substance that is compact, hard, and movable. 1. A rock is a naturally formed hard or soft substance of one or more minerals.
2. Stone is formed from rocks. 2. Smaller stones combine to form rocks.
3. Stone is simply a small piece that can be held in hand. 3. A huge piece of stone that is challenging to hold in hand is called a rock.
4. Compared to rock, a stone is small. 4. In comparison to stone, a rock is large.
5. One can move a stone easily. 5. Rock is not movable.
6. A stone is often solid and hard. 6. Rocks can be both soft and hard.
7. In construction projects, stones are used to build lintels, claddings, kitchen tops, and much more. 7. Rock was first converted into stones and then used in the construction sector.

Difference Between Sedimentary Rock, Igneous Rock, and Metamorphic Rock

Parameter Sedimentary Rock Igneous Rock Metamorphic Rock
1. Definition The aggregation or deposition of sedimentary elements produces sedimentary rock. Igneous rocks are a significant type of rock that is created when lava or magma solidifies. Metamorphic rocks are created when one rock type is changed into another.
2. Formation Sedimentary rocks form from sediment, minerals, or organic stuff. Igneous rocks are created from magma or lava. Metamorphic rocks can originate from igneous, sedimentary, or existing metamorphic rocks.
3. Occurrence Almost 8 % of the Earth's crust is composed of sedimentary rocks. About 80 % of the Earth's crust consists of igneous rocks. Around 12 % of the Earth's surface is composed of metamorphic rocks.
4. Examples Clay, sandstone, siltstone, shale, limestone, breccia, etc. Granite, gabbro, obsidian, pegmatite, dunite, basalt, basalt porphyry, etc. Graywacke, schist, gneiss, serpentine, quartzite, marble, slate, etc.

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