Igneous Rocks

Igneous Rocks I. Formation of Igneous Rocks Intrusive igneous rocks are formed when magma hardens beneath Earth’s surface. Obvious crystals/mineral grains. Takes a long time to form. 2. Extrusive igneous rocks are formed when lava hardens above Earth’s surface. No obvious crystals. Takes a relatively short amount of time. http://www.classzone.com/books/earth_science/terc/content/investigations/es0603/es0603page05.cfm?chapter_no=investigation

Igneous Rocks II. Classification of Igneous Rocks Igneous rocks can be classified based on their: texture and composition. 1. Textures • Coarse-grained texture is caused by slow cooling resulting in larger crystals. • Fine-grained texture is caused by rapid cooling resulting in smaller, microscopic mineral grains.

Igneous Rocks Texture (continued) • Glassy texture is caused by extremely rapid cooling. Porphyritic texture is caused by slow then rapid cooling. You will see a fine-grained texture with larger crystals within the rock. Vesicular – a texture that has lots of vesicles (holes) from escaping gas.

Course-Grained Igneous Texture Obvious crystals

Fine-Grained Igneous Texture No obvious crystals

Obsidian Exhibits a Glassy Texture. Extremely rapid cooling No crystals

Both fine and coarse-grained = porphyritic porphyritic texture Fine-grained with some crystals

Both fine and coarse-grained = porphyritic vesicular texture Lots of vesicles (holes) from gas

Igneous Rocks 2. Composition - What the rock is made of • Granitic composition rocks are made mostly of light-colored minerals like quartz and feldspar. • Basaltic composition rocks are made mostly of dark-colored silicate minerals like pyroxene.

Igneous Rocks b. Composition (continued) • Andesitic composition rocks are between granitic light-color minerals and basaltic composition dark-colored minerals. • Ultramafic composition rocks are made mostly from dark and heavy minerals like olivine.

Classification of Igneous Rocks

Classification of Igneous Rocks TEXTURE DESCRIPTIONS

Classification of Igneous Rocks WHAT ROCK LOOKS LIKE

Classification of Igneous Rocks HOW LIGHT OR DARK THE ROCK IS

Classification of Igneous Rocks NAME OF ROCK

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Add these notes to your TOC Igneous Rocks Classification

At lab today: Look at rock samples- Sketch and color/shade each rock make/ write observations about each rock in the table Such as: texture, composition (colors), determine type of igneous rock (intrusive, extrusive); record if there are vesicles, etc Name the rock Add a row for Glassy Texture

Period 2 Lab 1 – Jam, Aiden H, Ari Lab 2 – Delaney, Sophia Lab 3 – Raegan, Dylan Y, Dylan F Lab 4 – Kyla, Jordan, Ella D Lab 5 – Ronald, Smiley, Hunter, Abby Lab 6 – Dustin, Luke, Kolton Lab 7 – Parker, Maddisyn, Lili Lab 8 – Lily P, Ella M, Elizabeth

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