Midterm II Outline
November 24, 2013
Geology Midterm II outline
* Igneous Rock – Rock that forms when hot molten (magma or lava) cools and freezes solid.
A. The difference between intrusive and extrusive rocks is that extrusive rocks are rocks formed by the freezing of lava above ground while intrusive rocks solidify inside the earth.
B. Magma – Molten rock under the earths crust.
i. The heat from the magma comes from deep within the core. The geothermal gradient shows rate of change in temperature in depth.
ii. Volatiles are elements such as H2O and CO2 that evaporate easily and can exist in gaseous forms at the earth’s surface.
iii. Evolution of Magma
1. Partial melting is the melting in a rock of the minerals with the lowest melting in temperatures, while other minerals remain solid.
2. Fractional crystallization is the process by which a magma becomes progressively more silitic as it cools, because early-formed crystals settle out.
3. The Bowen Reaction Series is the sequence in which different silicate crystallize during the progressive cooling of a melt.
iv. Viscosity – The resistance of material to flow.
4. Hotter magma is less viscous than cooler magma. It also depends on the composition; mafic lavas are less viscous than felsic lavas, similarly, magma with a high volatile content are less viscous than (volatile-free) magmas.
v. Intrusion – Rock formed by the cooling of magma underground.
5. Country rock – the surrounding rock to mineral deposits, intrusions, etc.
6. Chamber – A magma chamber is a large underground pool of liquid rock found beneath the surface of the Earth.
7. Neck – A column of igneous rock formed by coagulation of lava in the conduit of a volcano and later exposed by the removal of surrounding rocks.
8. Sill – An approximate horizontal sheet of igneous rock intruded between older...