Igneous Rocks

How are igneous rocks formed? Key Concept #1 How are igneous rocks formed? the melting and solidification of magma

How to Tell Igneous Rocks The key concept about all igneous rocks is that they were once hot enough to melt. The following traits are all related to that: •Because their mineral grains grew together tightly as the melt cooled, they are relatively strong rocks. •They're made of primary minerals that are mostly black, white or gray. Any other colors they may have are pale. •Their textures generally look like something that was baked in an oven. The even texture of coarse-grained granite is familiar from building stones or kitchen counters. Fine-grained lava may look like black bread (including gas bubbles) or dark peanut brittle (including larger crystals). How to Tell Igneous Rocks The key concept about all igneous rocks is that they were once hot enough to melt. The following traits are all related to that: •Because their mineral grains grew together tightly as the melt cooled, they are relatively strong rocks. •They're made of primary minerals that are mostly black, white or gray. Any other colors they may have are pale. •Their textures generally look like something that was baked in an oven. The even texture of coarse-grained granite is familiar from building stones or kitchen counters. Fine-grained lava may look like black bread (including gas bubbles) or dark peanut brittle (including larger crystals). How to Tell Igneous Rocks The key concept about all igneous rocks is that they were once hot enough to melt. The following traits are all related to that: •Because their mineral grains grew together tightly as the melt cooled, they are relatively strong rocks. •They're made of primary minerals that are mostly black, white or gray. Any other colors they may have are pale. •Their textures generally look like something that was baked in an oven. The even texture of coarse-grained granite is familiar from building stones or kitchen counters. Fine-grained lava may look like black bread (including gas bubbles) or dark peanut brittle (including larger crystals).

Name four places where igneous rocks form Igneous Rocks: Key Concept #2 Name four places where igneous rocks form

Volcanoes Rifts/Ridges

Igneous rocks form at four main places on Earth: •At divergent boundaries, like mid-ocean ridges, plates rift apart and form gaps that are filled by magma. •Subduction zones occur whenever a dense oceanic plate is subducted underneath another oceanic or continental plate. Water from the descending oceanic crust lowers the melting point of the above mantle, forming magma that rises to the surface and forms volcanoes. •At continental-continental convergent boundaries, large landmasses collide, thickening and heating the crust to melting. •Hot spots, like Hawaii, form as the crust moves over a thermal plume rising from deep in the Earth. Hot spots form extrusive igneous rocks.

What determines crystal size? Igneous Rocks: Key Concept #3 What determines crystal size?

cooling time

crystal size cooling time

Large Crystals Indicate long cooling time Small Crystals Indicate short cooling time

What’s the difference between extrusive and intrusive igneous rocks? Igneous Rocks: Key Concept #4 What’s the difference between extrusive and intrusive igneous rocks?

Intrusive Extrusive form on or near the surface (small crystals) form below the surface (large crystals)

Igneous Rocks: Key Concept #5 Characteristics used to classify igneous rocks

Key Concept #5 texture glassy } extrusive fine Characteristics used to classify igneous rocks texture glassy } extrusive fine

Key Concept #5 texture coarse } intrusive very coarse Characteristics used to classify igneous rocks texture coarse } intrusive very coarse

Key Concept #5 color dark light Characteristics used to classify igneous rocks color dark light

low high Key Concept #5 density Characteristics used to classify igneous rocks density low high

Key Concept #5 composition mafic contains Fe and Mg felsic contains Al Characteristics used to classify igneous rocks composition mafic contains Fe and Mg felsic contains Al

Key Identifying Features of Igneous Rocks Igneous Rocks: Key Concept #6 Key Identifying Features of Igneous Rocks

the grains have been melted and are now physically connected Glassy Texture usually black in color Interlocked Grains the grains have been melted and are now physically connected

Igneous Rocks as Resources