Igneous Rocks

I. Formation of Igneous Rocks Igneous Rocks 1.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. =investigation

II. Classification of Igneous Rocks Igneous Rocks 1. Texture… (3 kinds of texture) Igneous rocks can be classified based on their composition and texture. Coarse-grained texture is caused by slow cooling resulting in larger crystals. Fine-grained texture is caused by rapid cooling resulting in smaller, often microscopic mineral grains.

Igneous Rocks Texture (continued) Glassy texture is caused by extremely rapid cooling.

Course-Grained Igneous Texture

Fine-Grained Igneous Texture

Obsidian Exhibits a Glassy Texture.

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.

Basalt

Classification of Igneous Rocks

Look at 4 rock samples- –Sketch and make/ write observations about each on your notes page Such as: texture, composition (colors), determine type of igneous rock (intrusive, extrusive); record if there are pores, etc Assignment