University:
University of Houston
Course:
PHYS 4356 | Particle and Nuclear Physics
Academic year:

2022
Views:

68

Pages:

12
Author:

Eliana Frazier

Three Types of Rocks Igneous Sedimentary Metamorphic 2 Magma and Igneous Rock • Magma forms from the partial melting of rock in the subsurface. – Composed of mainly silicon and oxygen, so when it cools it crystalizes to an igneous rock composed of silicate minerals – Magma at the surface is called lava. • Igneous rock forms as magma cools and minerals crystallize from the magma. – Composed of silicate minerals 3 Magma Consists of Three Components – Liquid portion = the melt • The liquid is a silicate melt (not water based) • Composed of mostly Si and O. – Solids, if any, are crystals of silicate minerals – Volatiles - dissolved gases in the melt that volatilize from the magma at low near-surface pressures Most common volatiles in magma • water vapor (H2O) • carbon dioxide (CO2) • sulfur dioxide (SO2) 4 Lava • Lava is magma that comes to the surface. • Magma most often comes to the surface at – subduction zones – spreading margins – hot spots. 5 Formation of igneous rock from magma crystallization Igneous Features and Landforms 6 The type of Igneous Rock depends on where it crystalizes (solidifies, turns to a solid) • Volcanic rocks or extrusive igneous rocks- are rocks that formed from magma that crystalizes at the surface • Plutonic rocks or intrusive igneous rocks - are rocks that formed from magma that crystalizes at depth 7 Crystallization occurs as magma cools and forms interlocking crystals. We refer to these as crystals even though, in general, you cannot see individual crystal faces. When crystals grow in a confined space they grow into one another (interlock), so the crystal faces do not form. 8 The size of the interlocking crystals gives information on the rate of crystal growth The slower the magma cools, the slower the crystals form, and thus the larger they can grow. Slower cooling 9 The size of the interlocking crystals gives information on depth of origin • Large crystals form in intrusive igneous rocks, because they crystalize at depth and thus cool very slowly • Small crystals (you can barely see without magnification), form in extrusive igneous rocks because the magma can cool rapidly. • Glass (no crystals) forms in extrusive igneous rock subjected to extremely fast cooling – This occurs when lava is ejected into the air or flows into water – Obsidian, pumice, volcanic ash, scoria obsidian 10 Intrusive Extrusive large crystals small crystals Fig. 5.111 Types of glassy volcanic rocks Obsidian - volcanic glass formed as lava flows into water and cools quickly Pumice - intertwined glass ejected from the volcano Scoria – extremely vesicular volcanic ejecta Volcanic Ash – very small loose pieces of volcanic glass ejected from volcano Tuff – a rock formed from compacted volcanic ash 12 Pyroclastic • Pyroclastic is any rock fragment ejected from the volcano • pumice, scoria, ash, cinder, volcanic bombs • can be fine ash mixed with large angular blocks embedded in the ash 13