Igneous Rocks

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These form from hot, liquid rock ( @ 1500 oc ) which cools. When this happens, crystals grow from the chemicals in the liquid. They form both from either Magma [ inside the Earth ], or Lava [ on the surface of the Earth ].

Click on the rock names in the picture below . . .

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Granite & Rhyolite:

 Both of these contain similar chemicals [ lots of Silicon, making an acid magma ]. This makes them both light coloured.

Granite:

Large crystals - cooled slowly in the earth, so the crystals had time to grow.

  Granite.jpg (33768 bytes)

Rhyolite:

Small crystals - cooled quickly on the surface of the earth, so the crystals did not have much time to grow.  

 

Rhyolite.jpg (29681 bytes)

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Basalt:

Much like Rhyolite, small crystals - cooled quickly on the surface of the earth, so the crystals did not have much time to grow. Unlike Granite & Rhyolite, contain different chemicals [ much less Silicon, making an alkaline magma ]. This makes it very dark coloured.

Basalt.jpg (47617 bytes)

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Small Crystals
Small Crystals

( fast cooling )

 Large Crystals

( slow cooling )
Alkaline Magma

( dark colour )

 Basalt Gabbro
Acid Magma

( light colour )

 Dolerite Granite
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