Section 1
Molten Rock Creates Different Igneous Rocks
Magma cooling slowly beneath Earth's surface forms intrusive rocks with large crystals, while lava cooling quickly on the surface creates extrusive rocks with small crystals.
In this Grade 6 Earth Science lesson from Chapter 3: Rocks, students learn how igneous rocks form from molten rock, distinguishing between intrusive igneous rocks that cool within Earth and extrusive igneous rocks that cool at the surface. Students explore why silica content is used to classify igneous rocks and how cooling time determines crystal size, using granite and rhyolite as real-world examples of rocks with the same mineral composition but different crystal structures. The lesson also explains why igneous rocks form durable, long-lasting landforms.
Section 1
Molten Rock Creates Different Igneous Rocks
Magma cooling slowly beneath Earth's surface forms intrusive rocks with large crystals, while lava cooling quickly on the surface creates extrusive rocks with small crystals.
Section 2
Silica Content Determines Rock Color
Igneous rocks with high silica content, like granite and rhyolite, appear light-colored. Rocks with low silica, such as basalt and gabbro, look dark. Scientists use color to estimate composition.
Section 3
Igneous Rocks Shape Earth's Landforms
Hard, resistant intrusive formations remain after surrounding weaker rock wears away. Extrusive lava builds volcanoes and plateaus, with silica-poor lava flowing farther and silica-rich lava creating steeper slopes.
Section 4
Scientists Measure Irregular Areas Using Grids
Geologists estimate areas with irregular boundaries, like lava flows, by counting grid squares. Complete squares plus fractions of partially covered squares help calculate total area in square kilometers.
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Section 1
Molten Rock Creates Different Igneous Rocks
Magma cooling slowly beneath Earth's surface forms intrusive rocks with large crystals, while lava cooling quickly on the surface creates extrusive rocks with small crystals.
Section 2
Silica Content Determines Rock Color
Igneous rocks with high silica content, like granite and rhyolite, appear light-colored. Rocks with low silica, such as basalt and gabbro, look dark. Scientists use color to estimate composition.
Section 3
Igneous Rocks Shape Earth's Landforms
Hard, resistant intrusive formations remain after surrounding weaker rock wears away. Extrusive lava builds volcanoes and plateaus, with silica-poor lava flowing farther and silica-rich lava creating steeper slopes.
Section 4
Scientists Measure Irregular Areas Using Grids
Geologists estimate areas with irregular boundaries, like lava flows, by counting grid squares. Complete squares plus fractions of partially covered squares help calculate total area in square kilometers.
Book overview
Jump across lessons in the current chapter without opening the full course modal.
Continue this chapter