Igneous Rocks “Liquid Hot Magma!”
Igneous Rocks • Rocks formed from cooling of lava or magma • Lava-Melted rock erupted from volcanoes and deposited on the earth’s surface. Cools quickly. • Magma-Melted rock that sits inside the earth in a magma chamber. Cools slowly. Magma Chamber
Types of Igneous Rocks • 2 major types: Intrusive and Extrusive • Intrusive igneous rocks cool and harden inside the earth. • Extrusive igneous rocks cool and harden on the earth’s surface or outside the earth.
Intrusive Igneous Rocks • Form when magma cools before reaching the surface. • Cool very slowly • Intrusive igneous rocks have large, interlocking crystals because they cooled slowly inside the earth. • Examples are Granite, Gabbro, Diorite, and Unakite (Virginia’s State Rock!) Granite • Unakite
Extrusive Igneous Rocks • Form when lava erupts and hardens on the surface. • Cool very quickly • Extrusive igneous rocks have fine (small) to no crystal grains at all. • A rock with no visible grains is called a volcanic glass (examples are pumice and obsidian). • Examples are Obsidian, Pumice, Scoria, Basalt, Tuff, Porphyry (cools inside then erupts), Rhyolite, Andesite. Rhyolite Obsidian
Texture of Igneous Rocks • Grain Size (Glassy, Fine, Medium, Coarse) • Grain Shape (Irregular, Angular) • Sorting: • Glassy: Looks like glass (Obsidian, Pumice) • Aphanitic: Can’t see crystals (Scoria, Tuff) • Porphyritic: Large crystals in fine matrix (Porphyry) • Phaneritic: Medium to Large interlocking crystals (Granite, Diorite, Gabbro)
Textures Glassy Phaneritic Aphanitic Porphyritic
Vesicles • Vesicles are holes found ONLY in Igneous rocks. • Formed from trapped gasses when lava erupts • Examples: Scoria, Pumice, Basalt (sometimes)
Tectonic Plate Boundaries • Places where tectonic plates converge, diverge, or slip past each other.
Igneous Rocks form at Convergent Boundaries • Ocean-Continent Convergent Boundary. • Forms volcanoes like those in Washington State.
Igneous Rocks form at Divergent Boundaries • Divergent Boundary or Spreading Ridge • Forms volcanoes like those that make up Iceland and the mid-Atlantic Ridge.
Igneous Rocks Form at Hot Spots • A hot spot is where magma rises to the surface in the middle of a plate and not a plate boundary. • Forms volcanoes like those in Hawaii or Yellowstone.
Hot Spots Hawaii Yellowstone