Igneous Rocks

By. Group 1 Jackie, Andrew, Brittany, and Jessica.

What is an Igneous Rock?

• An Igneous Rock are one of the three main rock types. Rocks that form when molten cools and crystallizes.

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Igneous Rock Facts

• Igneous Rocks make up approximately 90% of the upper part of the earths crust, but their great abundance is hidden on the earth’s surface by a relatively thin but widespread layer of sedimentary and metamorphic rocks.

Classifying Igneous Rocks• Igneous rocks are based on mineral

composition (Color), and texture (Crystal Size).

• Differences in magma composition can be observed in the rocks that form when the magma cools and crystallizes.

• Texture is used to subdivide igneous rocks into four groups Glassy, Fine-grained, Coarse-grained, and Very coarse-grained.

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Mineral Composition

Rock type can be determined by estimating the relative percentages of minerals in the rocks.

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Intrusive Rocks• An intrusive igneous rock is when magma rocks is underground, cools and hardens.

• Intrusive igneous rocks form in magma chambers that are deep underground.

• Many kilometers below the Earth surface, molten rock called magma flows into cracks or underground chambers.

• There, the magma sits, cooling very slowly over thousands to millions of years. As it cools, element combine to form common silicate minerals, the building blocks of igneous rocks.

• The mineral crystals within them are large enough to see without a microscope.

• There are many different types of intrusive igneous rocks but granite is the most common type.

Extrusive Rocks

• Extrusive igneous rock forms when molten rock reaches the earth's surface and cools. Air and moisture cool the lava rapidly.

• We can see holes left in the rock where the bubbles of gas were located. These rocks are also known as vesicular rocks.

Vesicular Rocks

• Magma contains dissolved gases that escape when pressure on the magma lessens.

• The holes in the rocks are called vesicles.

• Example Pumice-QuickTime™ and a

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