The interior of the planet is hot. Geothermal Gradient: the heat within the planet steadily boosts with depth; theheat is from radioactive decay and also remnant warmth of the Earth"s formation.

Magma is molten rock material. As magma cools the aspects within the magma combine and also crystalize into minerals that kind an igneous rock.

You are watching: Which igneous rock cools the fastest

Magmacools either listed below the surface or in ~ the surface (magma that reaches the surface is referred to as lava).

As magma cools igneous rock is formed. There room two types of igneous rock:

1) Extrusive: magma reaches the surface ar of the Earth prior to cooling and also the lava cools rapidly.

2) Intrusive: magma cools under the Earth"s surface. The magma cools really slowly.

As magma cools mineral are created into an interlocking setup prgimpppa.orgcing an igneous rock.


As magma cools that undergoes reactions that type minerals. The rate of cooling is really important. If the magma cools slowly then the reactions proceed for a longer period of time and the resulting mineral crystals (grains) end up being large. If the magma cools swiftly then the reaction are much quicker and also the mineral crystals (grains) space smaller.

Igneous rocks will have actually a distinctive appearance (this is referred to as texture) based upon the rate of cooling (fast or slow).

Textural terms for igneous rocks:

1. Phaneritic (coarse grained): rocks room composed that mineral grains large enough to it is in seen v the unaided eye. Indicitive of slow-moving cooling, commonly deep within the Earth.


See more: Why Is Convection More Important Than Conduction In The Troposphere ?

Aphanitic (fine grained): rocks space composed that mineral seed too little to be viewed by the unaided eye. Indicitive of much faster cooling, generally at or close to the Earth"s surface.

3. Glassy: magma cooled so conveniently that decision formation might not occur. Indicative of practically instant cooling in ~ the Earth"s surface.

4. Porphorytic: huge mineral cyrstals surrounding by a good grained matrix (background). This texture creates when sluggish cooling starts to kind large mineral crystals. Prior to the magma is fully cooled the magma (and its huge mineral grains) moves closer come the surface and finishes cooling in ~ a much more rapid pace.

Igneous rocks have actually a selection of chemical composition.

1. Sialic (granitic) or felsic: rocks have highest silica, save on computer feldspar and also ferromagnesium minerals. Rocks room light in color.

2. Intermediate (andesitic): rocks have actually less silica, save on computer feldspar and ferromagnesium minerals. Rocks are tool gray in color.

3. Mafic (basaltic): rocks have higher amounts that ferromagnesium minerals and also less silica and also feldspar. Rocks room dark in color, black color or dark gray.

4. Ultramafic: highest amount that ferromagnesium minerals and least quantity of silica. Rocks room usually a dark green to green-black.

Classification that Igneous Rocks

Igneous rocks room classified by both texture and composition. Friend will learn to identify common igneous rocks in lab.

intrusive (phaneritic)granitedioritegabbro
extrusive (aphanitic)rhyoliteandesitebasalt