Rocks~Igneous Rocks form from molten rock~ http://www.videojug.com/film/geology-igneous-rocks http://www.ehow.co.uk/video_4774969_identifying-igneous-rocks.html
Vocabulary • Magma • Molten rock beneath Earth’s surface • Lava • Molten rock that reaches Earth’s surface through a volcano
Igneous Rocks… Formation Cooling Time Crystal Size Mineral Composition Color Origin Igneous Rocks are classified on what minerals make up the rock and the size of mineral crystals.
Intrusive Forms when magma cools withinEarth Magma cools slowly being exposed to high temperatures Reach surface when forces inside Earth push rocks up & wind and water break apart/carry away surface rocks Extrusive Forms when lava cools on Earth’s surface Lava cools quickly being exposed to cool temperatures Reach surface through volcanoes erupting Origin of Igneous Rocks Igneous rocks are classified as INTRUSIVE or EXTRUSIVE
Intrusive Igneous Rocks Forms from magma within Earth’s surface Granite Diorite Gabbro Peridotite Pegmatite Anorthosite
Extrusive Igneous Rocks Forms from lava on Earth’s surface Basalt Pumice Obsidian Rhyolite Scoria Andesite
Textures of Igneous Rocks Texture of an igneous rock is determined by the size of its mineral crystals. Size of mineral crystals depends on how quickly the magma or lava cools.
Intrusive Interior of Earth is HOT High Temperatures allow magma to cool SLOWLY Slow cooling allows time for LARGE mineral crystals to form Extrusive Surface of Earth is COOL Lower temperatures cause the lava to cool QUICKLY No time for large mineral crystals to form so there are SMALL mineral crystals Textures of Igneous Rocks
Composition of Igneous Rocks Texture is not enough to identify an Igneous Rock. Some Igneous Rocks have similar textures. Composition is based on Silicate levels. Estimate SILICATE level by COLOR • LIGHT COLOR HIGH LEVELS OF SILICA • LOW LEVELS OF SILICA DARK COLOR Granite/Rhyolite Gabbro/Basalt Silica: Compound made up of silicon and oxygen which geologists use to classify rocks