Igneous Rocks An igneous rock. Extrusive vs. Intrusive Igneous Rocks Intrusive (plutonic) rock… Intrusive rocks are igneous rocks that have cooled slowly.

Igneous Rocks

An igneous rock

Extrusive vs. Intrusive Igneous Rocks

Intrusive (plutonic) rock…

Intrusive rocks are igneous rocks that have cooled slowly over time.

Batholiths, laccoliths, dikes and sills are examples of igneous intrusions.

Extrusive (volcanic) rock is one that forms from the cooling of lava (liquid rock) found at Earth’s surface.

Extrusive rocks… In

trus

ions

Extr

usio

ns

Formation of Igneous Rocks

Igneous rocks…

Most igneous rocks…

As an igneous rock cools into a solid form, different minerals form crystals that are inter-grown with other mineral crystals. This is known as crystallization.

Inter-grown crystals of several minerals formed by

crystallization.

Formation of Igneous Rocks – Crystal Size and Texture

The texture of an igneous rocks and the type of crystals it exhibits depends on the environment in which it had formed.

GRANITE GABBROGranite and Gabbro are both examples of

coarse-textured igneous rocks.

Both rocks have very large crystals that are

easy to see.

The development…

Coarse-grained igneous rocks cooled deep within the lithospshere (intrusions) where the temperature and

pressure are higher than that of Earth’s surface.

Formation of Igneous Rocks – Crystal Size and Texture

The development…

Fine-grained, igneous rocks…

Some fine-grained, igneous rocks have vesicles – large air pockets that formed within the rock when it is cooled quickly. Sometimes igneous rocks cool so

quickly that mineral crystals do not have time to form. Instead igneous rocks form a non-crystalline solid known as glass.

RHYOLITE BASALTOBSIDIAN

Rhyolite and Basalt are both examples of fine-textured igneous rocks.

Both rocks have very small crystals that can only be seen through magnification.

vesicles

glassy texture

Identification of Igneous Rocks

RT = Pg. 6

Identification of Igneous Rocks

Which igneous rock is intrusive and has crystal sizes greater than 10 mm?

Describe RHYOLITE.