Igneous Rocks: Formation, Types, Textures, and Characteristics - Prof. D. Kelley, Study notes of Geology

Download Igneous Rocks: Formation, Types, Textures, and Characteristics - Prof. D. Kelley and more Study notes Geology in PDF only on Docsity! CH 4 IGNEOUS ROCKS - Form by solidification of magma or molten (liquid) rock. - Most abundant igneous rock is basalt. 95% of crust is igneous rock. 75% of surface is sedimentary rock. All oceanic crust is igneous rock. MAGMA:  The earth is mostly solid. Therefore, magma forms within the Earth through melting.  Temperatures high enough to promote melting to produce basalt occur in the mantle.  Magmas ascend because silicate liquids are less dense than equivalent solid rocks.  Some magma reaches the surface and is extruded.  Most magma ponds and solidifies within the mantle or crust and is intruded. EXTRUSION OF MAGMA:  Magma can be extruded gently as lava or explosively as pyroclastic material. The magma cools and solidifies at earth’s surface.  Fine-grained texture. INRTUSION OF MAGMA:  Batholith : large body with irregular contacts (contact with rock already in place.)  Sill : Intrusive sheet approximately parallel to Earth’s surface. (horizontal sheet)  Dike : intrusive sheet approximately perpendicular to Earth’s surface. (vertical sheet)  Country Rock : crust that everything is being attributed to.  Volcanic Rock : eroded remnant of a volcano.  Intrusive igneous bodies are exposed to the surface by erosion. INTRUSIVE VS EXTRUSIVE:  Texture – Fine grain (extrusive), Coarse grained (intrusive). Overall appearance of rock: mainly size and shape of grains. COOLING AND SOLIDIFICATION:  Magma cools and solidifies. In most cases solidification involves formation and growth of crystals.  As solidification begins, submicroscopic nuclei form in the melt.  For these to grow into larger crystals, atoms must diffuse through the melt and become attached to the solid.  Diffusion takes time – it takes longer to grow large crystals than to grow small crystals.