Igneous Rocks CH 3 Prentice Hall p. 78-81

Igneous Rocks Form from lava or magma Made of mineral crystals Classified according to: Origin Texture Mineral Composition

Origin of Igneous Rocks Classified according to where they formed. Intrusive Extrusive

Origin of Igneous Rocks Intrusive Forms when magma hardens beneath the Earth’s surface. Granite Makes up most of the continental crust.

Origin of Igneous Rocks Extrusive Forms from lava that erupted onto Earth’s surface. Basalt Forms much of the ocean crust.

Which is a way to identify if a rock is Igneous? Streak B Origin C Solid D Hardness

Igneous Rock Textures Slowly cooling, large crystals Example: Granite Coarse Grained Slowly cooling, large crystals Example: Granite Fine Grained Lava cools quickly Forms smaller crystals. Porphyritic Both textures – large AND small crystals. Cools slowly, then rapidly. No Crystals Rock cools too quickly for crystals to form.

What is a Crystal? A solid in which the atoms are arranged in a pattern that repeats again and again.

Igneous Rock Textures Depends on the size and shape of it’s mineral crystals. Coarse Grained Porphyritic Fine Grained No Crystals

In your tray, what is the texture of sample… Coarse-grained B Fine-grained C Porphyritic D No visible crystals

Mineral Composition Most of Earth’s rocks contain silica (silicon dioxide, SiO2) High Silica (Felsic) Forms light colored rocks. Granite Dark to light gray, red and pink. Low Silica (Mafic) Forms dark colored rocks. Basalt Contains dark colored minerals. No quartz.

Igneous Rock Chart Low Density High Felsic (High) Silica Mafic (low) Origin Intrusive (Magma) Coarse Grained Granite Continental Crust Gabbro Both Porphyritic Large crystals with small crystals Scattered on top. Extrusive (Lava) Fine- Grained Rhyolite Basalt Ocean No Crystals Pumice Obsidian

Which rock likely has the most silica? B C

Igneous rocks are useful because they are hard, durable and dense Uses of Igneous Rocks Granite - building materials Obsidian - sharp tools Basalt - gravel, construction Pumice - used for cleaning and polishing Igneous rocks are useful because they are hard, durable and dense

Class Work Examine 5 Igneous Rocks and write down their texture (Fine-grain, Coarse-grain, Porphyritic, No Grain) Read the textbook, pages 78-81 Answer Questions 1 – 4 on page

Silica Content Felsic Mafic Intermediate Basalt Gabbro Granite Rhyolite Mafic Basalt Gabbro Intermediate Diorite Andesite