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from Wenatchee Valley College, Creative Commons
Intrusive Igneous Rocks
Intrusive Igneous Rocks
Igneous rocks that form inside the Earth’s crust are called intrusive igneous rocks. Granite (left) is a common example of an intrusive igneous rock... you may recognize it from kitchen countertops! Intrusive rocks cool slowly, and therefore have time to grow large crystals that are visible.
Extrusive Igneous Rocks
Extrusive Igneous Rocks
Igneous rocks formed outside of the Earth’s crust are called extrusive igneous rocks. Basalt and pumice (right) are two examples of extrusive igneous rocks. Extrusive igneous rocks usually form when lava cools quickly, which can create features like gas bubbles and fine-grain textures.
from Idaho State University
Types of Sedimentary Rocks
Types of Sedimentary Rocks
Clastic
Clastic
Clastic sedimentary rocks form from many different pieces of other rocks. The sandstone and conglomerate samples (above) are made from small chunks of rock that become stuck together.
Chemical
Chemical
Chemical sedimentary rocks, like this limestone (above), are made when water leaves behind chemical compounds or minerals on a surface that harden together into a single rock formation.
Organic
Organic
Organic sedimentary rocks form when materials from living organisms, such as shells or plant leaves, are compressed into hard layers of rock. Peat and coal are well-known examples.
all from Idaho State University
Types of Metamorphic Rocks
Types of Metamorphic Rocks
Foliated
Foliated
Foliated metamorphic rocks have bands or layers. These layers form due to extreme heat and pressure deep underground, and always contain minerals with elongated structures. Gneiss (above, pronounced "nice") is a common example of this rock type. Can you see the bands?
Non-Foliated
Non-Foliated
Non-foliated rocks do not have bands or layers, and usually appear similar throughout or have a consistent pattern. They are also formed under high heat and pressure, but do not have the minerals needed to create bands. Marble (above) is a non-foliated rock used in countertops and sculptures.
both from Idaho State University
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