IGNEOUS ROCKS – Classified according to their origin, texture, and composition
Origin
Where do they form? (Define each and give 1 example of each)
Extrusive
Igneous
rock
Rock formed from lava that erupted onto Earth’s surface
Intrusive
Igneous
rock
Rock formed from magma that has hardened beneath Earth’s surface
Texture
Fine – Grained
How do they form and what sizes of crystals form?
Rapidly cooling lava forms fine-grained rocks with small crystals
Basalt—most common extrusive rock & most common rocks on Earth
Forms much of Earth’s ocean floor
Granite—most abundant intrusive rock on Earth’s continents
Forms the core of many mountain ranges
Ex. Basalt
Glassy texture, crystals too small to be seen without a microscope
Ex. Obsidian
Smooth, shiny texture like thick glass & cooled without forming crystals
Coarse – Grained
Slowly cooling magma forms coarse-grained rocks with large crystals
Ex. Granite
Crystals vary in size and color
Ex. Porphyry
Looks like gelatin with chopped fruit mixed in
Mineral Composition
What happens when
rocks are high in silica?
What happens when
rocks are low in silica?
Uses
Most of Earth’s minerals contain silica, a material formed from oxygen & silicon.
Forms light-colored rocks, like granite
Forms dark-colored rocks, like basalt
List at least 6 things that igneous rocks have/can be used for.
1. Statues—Granite
2. Bridges and public buildings—Granite
3. Paving streets with cobblestone—Granite
4. Curbstones, floors, kitchen countertops—Thin polished sheets of
Granite
5. Gravel for construction—Basalt
6. Cleaning and polishing—Pumice
7. Sharp tools for cutting and scraping—Obsidian
8. Starting vegetable gardens (fertilizer)—Perlite formed from heating
obsidian