Plutonic rocks are rocks formed when magma cools and solidifies below the earth's surface. ... This magma is under high pressure and takes a long time to cool, allowing time for the formation of large crystals. Therefore, plutonic rocks have coarse-grained crystals.

Why does plutonic rock have coarse grain?

Volcanic or plutonic.

In plutonic rocks, the small grain-size part of the rock (matrix) is phaneritic, and the large grain-size crystals just larger. The texture usually implies a change in the rate of cooling from slow to rapid.

Are plutonic rocks coarse-grained?

In the restricted sense, plutonic rocks are coarse-grained crystalline igneous rocks formed by consolidation of molten rock material or magma below the Earth's surface (Latin Pluto, god of the Underworld).

Why do plutonic intrusive rocks show coarse-grained textures?

If magma cools slowly, deep within the crust, the resulting rock is called intrusive or plutonic. The slow cooling process allows crystals to grow large, giving the intrusive igneous rock a coarse-grained or phaneritic texture.

What makes a rock coarse-grained?

Coarse-grained textures generally indicate magmas that slowly cooled deep underground. Slow cooling gives crystals enough time to grow to easily seen sizes (i.e., larger than 1 mm). The first-formed crystals tend to have regular shapes because they grow freely into the surrounding liquid.

Plutonic Igneous Rocks

What determines grain size of igneous rock?

Texture relates to how large the individual mineral grains are in the final, solid rock. In most cases, the resulting grain size depends on how quickly the magma cooled. In general, the slower the cooling, the larger the crystals in the final rock.

What can you tell about an igneous rock that is coarse grained?

Coarse-grained – The grains, or crystals, are big enough to tell what mineral each one is. The crystals are usually larger than 1 millimeter (larger than the point of a pen or pencil). They are commonly 1/8 to 1 inch long.

Why igneous intrusive rocks have a coarse grained texture while igneous extrusive rocks have a fine-grained texture?

Extrusive or volcanic rocks crystallize from lava at the earth's surface. The texture of an igneous rock (fine-grained vs coarse-grained) is dependent on the rate of cooling of the melt: slow cooling allows large crystals to form, fast cooling yields small crystals. ... Volcanic glass is called obsidian.

Why do igneous rocks have different textures?

Explanation: The faster the magma cools that smaller the crystals that are formed. Some magma from which the igneous rocks is form come from different combinations of remelted igneous rocks, metamorphic rocks and sedimentary layers. ... The different sources of the melted material affects the textures of the igneous rocks.

Do plutonic rocks have texture?

The main way to tell a plutonic rock is that it's made of tightly packed mineral grains of medium size (1 to 5 mm) or larger, which means that it has phaneritic texture. In addition, the grains are of roughly equal size, meaning that it has an equigranular or granular texture.

What does plutonic rock mean in geography?

intrusive rock, also called plutonic rock, igneous rock formed from magma forced into older rocks at depths within the Earth's crust, which then slowly solidifies below the Earth's surface, though it may later be exposed by erosion. Igneous intrusions form a variety of rock types. See also extrusive rock.

What type of texture do plutonic rocks have?

A phaneritic texture is developed by the slow cooling and crystallisation of magma trapped within the Earth's crust and is characteristic of plutonic rocks.

What is the coarse grained?

having a coarse texture or grain. indelicate; crude; vulgar; gross: a coarse-grained person with vulgar manners.

Why are extrusive rocks fine-grained?

Igneous rocks which form by the crystallization of magma at the surface of the Earth are called extrusive rocks. They are characterized by fine-grained textures because their rapid cooling at or near the surface did not provide enough time for large crystals to grow. ... The most common extrusive rock is basalt.

How do volcanic and plutonic rocks differ in texture?

Volcanic rocks and plutonic rocks differ mainly in that volcanic rocks form at the surface of a planet whereas plutonic rocks form beneath the surface. Plutonic rocks are also coarser grained, being made of large interlocking crystals whereas volcanic rocks are more fine-grained.

What is the texture of a igneous rock?

The texture of an igneous rock made up entirely of crystals big enough to be easily seen with the naked eye is phaneritic. Phaneritic texture is sometimes referred to as coarse-grained igneous texture. Granite, the most well known example of an intrusive igneous rock, has a phaneritic texture.

What do igneous rock textures say about the rock that formed?

The igneous texture tells us how the magma cooled and solidified. Magma can solidify into igneous rock in several different ways, each way resulting in a different igneous texture. Magma may stay within the earth, far below ground level, and crystallize into plutonic igneous rock (also known as intrusive igneous rock).

What is meant when referring to the texture of an igneous rock?

Andrew Alden. Updated November 05, 2019. The texture of a rock refers to the details of its visible character. This includes the size and quality and interrelations of its grains and the fabric they form. Larger scale features, such as fractures and layering, are considered rock structures in comparison.

What does the coarse and fine grain texture of the rocks indicate about the rocks formed and their respective cooling histories?

Phaneritic texture describes coarse grained rocks. They are characteristic of intrusive (plutonic) rocks, and have crystals that can be seen with the unaided eye. Indicates slow cooling history. ... These larger crystals are called phenocrysts, while the finer-grained matrix is referred to as the groundmass.

What is the difference between extrusive igneous rocks and intrusive igneous rocks?

Extrusive rocks are formed on the surface of the Earth from lava, which is magma that has emerged from underground. Intrusive rocks are formed from magma that cools and solidifies within the crust of the planet.

What igneous rocks are fine-grained?

• Dacite is a fine-grained, extrusive igneous rock that is usually light in color. ...
• Gabbro is a coarse-grained, dark-colored, intrusive igneous rock that contains feldspar, pyroxene, and sometimes olivine.

How are fine-grained igneous rocks formed?

Fine-grained igneous rocks form when lava cools quickly at Earth's surface.

What is the shape of igneous rocks?

Hence such rocks are fine-grained (aphanitic) or even glassy. Basalt is the most common extrusive igneous rock and forms lava flows, lava sheets and lava plateaus. Some kinds of basalt solidify to form long polygonal columns. The Giant's Causeway in Antrim, Northern Ireland is an example.

Are intrusive rocks coarse grained?

Intrusive rocks have a coarse grained texture. Extrusive Igneous Rocks: ... Quick cooling means that mineral crystals don't have much time to grow, so these rocks have a very fine-grained or even glassy texture. Hot gas bubbles are often trapped in the quenched lava, forming a bubbly, vesicular texture.