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.

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