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

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

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Magmacools either below the surface or at the surface ar (magma that reaches the surface ar is referred to as lava).

As magma cools igneous rock is formed. There are two species of igneous rock:

1) Extrusive: magma will the surface of the Earth before cooling and the lava cools rapidly.

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

As magma cools minerals are formed into an interlocking arrangement prtennis2007.orgcing an igneous rock.


As magma cools the undergoes reactions that kind minerals. The rate of cooling is really important. If the magma cools gradually then the reactions proceed for a longer duration of time and also the resulting mineral crystals (grains) become large. If the magma cools rapidly then the reaction are much quicker and also the mineral crystals (grains) space smaller.

Igneous rocks will have a distinctive figure (this is described as texture) based upon the price of cooling (fast or slow).

Textural terms because that igneous rocks:

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


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Aphanitic (fine grained): rocks space composed of mineral seed too little to be watched by the unaided eye. Indicitive of quicker cooling, usually at or near the Earth"s surface.

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

4. Porphorytic: huge mineral cyrstals surrounding by a well grained matrix (background). This texture develops when slow-moving cooling starts to kind large mineral crystals. Before the magma is totally cooled the magma (and its big mineral grains) moves closer come the surface and finishes cooling in ~ a more rapid pace.

Igneous rocks have actually a variety of chemical composition.

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

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

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

4. Ultramafic: highest possible amount the ferromagnesium minerals and least lot of silica. Rocks space usually a dark green to green-black.

Classification that Igneous Rocks

Igneous rocks room classified through both texture and also composition. You will discover to identify typical igneous rocks in lab.

intrusive (phaneritic)granitedioritegabbro
extrusive (aphanitic)rhyoliteandesitebasalt