Rocks

Igneous Rocks Intrusive: form when magma cools ___________ inside the Earth. Extrusive: form when lava cools ___________ on the Earth’s surface.

Texture of Igneous rocks Intrusive igneous rocks: Cool slowly Allows time for the minerals to form _________ crystals Rocks with large crystals have a _____________ texture Example: granite, gabbro

Granite Gabbro

Extrusive igneous rocks Cool _____________ Quick cooling doesn’t allow time for large crystals to form This produces a ___________ texture Example: basalt Extremely rapid cooling cause NO crystals to form Example: obsidian (volcanic glass) Sometimes gasses are trapped in cooling magma and form bubbles Example: pumice ,scoria

Basalt Obsidian

Pumice Scoria

Igneous Rock Structures Intrusion: underground rock mass made of intrusive rock Extrusion: surface rock mass of extrusive rock

Intrusions Batholith: Laccolith: ____________ intrusion Large underground mass of rock which may cover hundreds of miles Laccolith: Magma flows between rock layers and spreads upward, pushing the rock above into an ___________

Sill: Sheet of magma ________________rock layers and hardens They are always parallel to the ______________ rock layers Can be thin (few centimeters) or thick (several hundred meters)

Dike: Forms when magma forces its way into existing fractures Once magma hardens it is called a dike Dikes cut ___________ rock layers (perpendicular to them)

Extrusions Volcanic neck: Lava flow: Lava capped-plateau Solidified central shaft of a volcano Lava flow: Erratically shaped mass of extrusive rock Lava capped-plateau Lava that spreads over vast area and hardens