Igneous Rocks Igneous Rocks n n Igneous rocks

Igneous Rocks

Igneous Rocks n n Igneous rocks are any rock that forms from magma or lava. Igneous rocks may form on or beneath Earth’s surface.

Classifying Igneous Rocks n n n The name igneous comes from the latin word ignis, meaning “fire”. Igneous rocks are classified according to their origin, texture, and mineral classification. There are two types of igneous rock n n Extrusive Intrusive

Origin n n Extrusive igneous rocks are formed when lava erupts or flows above the Earth’s surface and cools forming a rock Quick cooling makes rocks with very little mineral crystals. Ø Basalt is the most common extrusive rock

Origin n n Intrusive igneous rocks forms when magma hardens beneath the Earth’s Crust. The cooling can take thousands or even millions of years, mineral crystals can grow quite large if space allows • Granite is the most abundant intrusive rock on Earth’s continents

Texture n Depends on the size and shape of the mineral crystals Ø n An exception to this rule are certain types of rock that have a texture like glass. Igneous rocks may have similar chemical compositions and yet be very different

Mineral Composition n Light colored rocks n n n Most of Earth’s minerals contain silica Magma high in silica usually forms light-colored rocks Granite ranges in color: light gray, red, pink, or nearly black. n Dark colored rocks n n Magma with a low silica content usually forms dark-colored rocks. Basalt has low silica content and also contains other darkcolored minerals

Uses of Igneous Rocks n Building materials More than 3, 500 years ago ancient Egyptians used granite for statues n About 600 years ago the Incas of Peru used granite and other igneous n U. S. granite is widely used to build bridges, public buildings, paving streets, counter tops etc… n n Tools n Obsidian was used by ancient native Americans for sharp tools for cutting and scraping.

Sedimentary Rocks n Stay tuned for another exciting day of notes when we discuss weathering and the formation of sedimentary rock.