Post on 19-Jan-2016
Formation and Characteristics
IGNEOUS ROCKS
Igneous rocks are formed from the crystallization of magma.
Molten rock can occur in three diff erent ways: Magma: molten rock below Earth’s surface Lava: magma on the Earth’s surface Pyroclastic material: (pyro=fire, clastic=debris)
Airborne lava that cools at it falls.
IGNEOUS ROCKS
When we talked about Earth’s crust we said that the most common elements were: Oxygen Silicon Aluminum Iron Magnesium Calcium Potassium Sodium
We said that the crust was mostly Silicate (SiO2) rocks, magma is classified by its Silica content.
MAGMA
Mafic magma (Basaltic) Thin and runny LOW silica content (<50%) LOW gas content HIGH in Ca, Fe, and Mg
Intermediate magma (Andesitic) Medium Consistancy MODERATE silica content (~60%) MODERATE gas content MODERATE amount of all crustal elements
MAGMA
MAGMA
Felsic magma (Rhyolitic) Thick and blocky HIGH silica content HIGH gas content LOW in Ca, Fe, and Mg HIGH in K and Al
Viscosity: the resistance of a liquid to flow. Very important for volcanic activity
MAFIC- low silica, low viscosity, runny, less violent eruptions FELSIC- high silica, high viscosity, thick, more violent eruptions
VISCOSITY OF MAGMA/ LAVA
98.5% of earths crust is made of only 8 elements! Oxygen and Silicon make up 75% Aluminum=8.1% Iron=5% Calcium=3.6% Sodium=2.8% Potassium=2.6% Magnesium=2.1%
Sooooooo, the type of rock created is mainly determined by: What elements are present during cooling How rapidly does the rock cool
Neatly, illustrated by Bowen’s reaction series.
IGNEOUS ROCK COMPOSITION
BOWEN’S REACTION SERIES
Igneous rocks are classified in two ways Texture Composition
Textures (How big are the mineral grains) Phaneritic: can be seen with naked eye different colored
and interlocking shapes
Aphanitic: mineral grains too small to be seen, microscopic
Porphyritic: two distinct sizes of mineral
IGNEOUS TEXTURES
Intrusive rock Cooled beneath Earth’s surface Cooled very slowly Higher temperature and pressure
PHANERITIC TEXTURE
Extrusive Igneous Rock Cooled on Earth’s surface Cooled relatively fast Lower temperature and pressure
APHANITIC TEXTURE
Complex coolingPartially cools below and above Earth’s surfaceDistinct crystal sizes
PORPHYRITIC TEXTURE
Igneous rocks are named by texture and mineral composition
COMPOSITION
Magmas have three main types Mafic Intermediate Felsic
Composition and cooling rate determine what minerals will form
Three types of igneous textures Phaneritic Texture Aphanitic Texture Porphyritic Texture
Put it all together and you can identify your igneous rock
SUMMARY