This is only an outline of the lecture. You will need to go to class
       to fill in the outline, although much of the relevant information is
       also in the text.
 
 

IGNEOUS ROCKS

             Igneous Rocks are crystallized from magma or lava:

             magma
 
 
 

             lava
 
 
 

             tephra
 

 ROCK CYCLE DIAGRAM

             Each type of rock can be transformed into any of the other rock types.

             Where does magma come from? The rock cycle diagram shows us
 
 
 
 

WHY DO ROCKS MELT IN THE EARTH?

             Temperature
 
 
 

             Percent Silica
 
 
 
 

             H2O
 
 
 
 

             Pressure
 
 
 
 

TEXTURES OF IGNEOUS ROCKS

             Plutonic Rocks:
 

             Phaneritic
 
 
 

             Pegmatite
 
 

             Volcanic Rocks:
 

             Aphanitic
 
 
 

             Porphyritic (porphyry)
 
 

             Vesicular, glassy, fragmental, pyroclastic...
 
 
 

IGNEOUS COMPOSITIONS

             The most important variable is percent silica.

             Minerals are a guide to percent silica, because
             percent silica is related to mineral structure.

             Silicate minerals:

             low silica............................................high silica

             olivine...pyroxene...amphibole...mica...quartz

             isolated... chain...dbl chain...sheet...framework

             [ Feldspar: aluminum in framework replaces some silica. ]

             Mafic rocks:
 
 
 

             Felsic rocks:
 
 
 
 

NAMES OF IGNEOUS ROCKS

             A rock's name depends on the minerals in it.

             High Si minerals........................Low Si minerals

             Felsic......Intermediate......Mafic......Ultramafic

             Plutonic rock names:
 
 

             __________ ___________ ___________ ___________

             Volcanic rock names:
 
 

             ___________ ___________ ___________ ___________

             Mineral content affects the over-all color of the rock.

             High Si minerals........................Low Si minerals
             light color rocks........................dark color rocks
 
 
 

HOW DOES MAGMA CRYSTALLIZE?

             Crystals don't all form at once. Some form at high temperature, and others form later as the magma cools.

             Low silica minerals crystallize first (at highest temperature).

             The approximate order of crystallization, which varies with composition, H2O and pressure, is

             BOWEN'S REACTION SERIES

             Discontinuous Series.............Continuous Series

             olivine                                                                                                                   Ca-plagioclase

                        pyroxene (augite)
                                                                                                                            Na-plagioclase
                                        amphibole (hornblende)

                                                             biotite mica
                                                                                                             K- feldspar
                                                                             muscovite mica

                                                                                               quartz
 
 
 

MINERALS MAKE THE ROCK

             Which minerals are present in the rock depends on the composition of the magma from which they formed.

             Ultramafic rocks form today only in the mantle.
             Peridotite is made of
 
 

             Mafic magma forms gabbro and basalt. The minerals in basalt and gabbro are:
 
 

             Intermediate magma forms diorite and andesite. The minerals in diorite and andesite are:
 
 

             Felsic magma forms granite and rhyolite. The minerals in granite and rhyolite are:
 
 
 

WHERE DOES MAGMA FORM?

             Magma forms in both the mantle and crust.

             Magma forms in various tectonic settings:

             1) Mid-Ocean ridges
             source of magma:
 
 
 

             why magma forms:
 
 
 

             magma composition:
 
 

             2) Subduction zones
             source of magma:
 
 
 

             why magma forms:
 
 
 

             magma composition:
 
 
 
 

             3) Hot spots: Ocean Islands [Hawaii...]
             source of magma:
 
 
 

             why magma forms:
 
 
 

             magma composition:
 
 

             4) Hot spots: Continental [Yellowstone...]
             source of magma:
 
 
 
 

             why magma forms:
 
 
 
 

             magma composition:
 
 
 
 

IGNEOUS INTRUSIONS

             These form when magma cools underground.

             Plutons: discordant intrusions
 
 
 
 
 

             Sills: concordant intrusions
 
 
 
 

             Dikes: (discordant) pathways of magma intrusion
 
 
 
 
 

             Veins: minerals crystallized from (hot) water solution. Often associated with plutons.
 
 
 
 

VOLCANISM

             Whether magma will stay in the ground, or erupt, is determined by three main factors.

             What makes volcanoes erupt?

             1) Silica content
 
 
 
 
 

             2) Vapor content (gasses, including H2O)
 
 
 
 
 

             Combination of high silica + high vapor content:
 
 
 
 

             3) Crystallization
 
 
 
 

TYPES OF VOLCANOES

    1. Shield volcanoes and lava plateaus

             rock name:
 

             volcano shape:
 
 
 
 

             lava characteristics:
 
 
 
 
 

             examples:
 
 
 

    2. Tephra cones (cinder cones)

             rock names:
 

             volcano shape:
 
 
 
 

             tephra characteristics:
 
 
 
 
 

             examples:
 
 
 
 
 

    3. Stratovolcanos (composite cones)
 

             rock names:
 

             volcano shape:
 
 
 
 

             lava and tephra characteristics:
 
 
 
 
 
 

             examples:
 
 
 
 

    4. Volcanic domes

             rock names:
 
 

             volcano shape:
 
 
 
 

             lava characteristics:
 
 
 
 
 

             examples:
 
 
 
 
 

    5. Calderas and craters

             These may occur in a number of types of volcanoes. Most volcanic mountains have small craters in the top.

             Calderas: definition:
 

             How formed:
 
 
 
 

             Types of associated volcanoes:
 
 
 
 

             Examples: