Upload
elizabeth-spackman
View
218
Download
0
Tags:
Embed Size (px)
Citation preview
Types of Igneous Rocks• Igneous rocks
are formed from the crystallization of magma• Igneous comes
from Latin ignis which means fire
• Lava is magma that flow out onto earth's surface
Types of Igneous Rocks Cont…
• Extrusive igneous rocks are fine-grained igneous rocks that cool quickly on earth’s surface • Pumice or obsididan
• Intrusive igneous rocks are coarse grained igneous rocks that cool slowly beneath the earth’s surface• Granite is the most common
• Studies of granite formations reveal they cut across other formations, evidence of intrusion
Composition of Magma Magma is a slushy mix of molten
rock, gases and mineral crystals Silica (SiO2) is the most abundant
mineral in magma and has the greatest effect on magma characteristics
Magma Formation Temperature,
pressure, water content and mineral composition affect magma formation
Temperature and pressure increase with depth in the Earth’s crust
Pressure increases a rocks melting pointo 1100 vs 1400
Magma Formation cont…
Rocks and minerals contain small percentages of water which decreases a rocks melting point
Minerals have different melting points
Rocks only melt at certain conditions MUST have the right temperature,
pressure, and mineral composition
How Rocks Melt Rocks are made of different minerals Minerals have different melting
points so parts of a rock will melt at different times
Partial melting is a process where some minerals melt at low temperatures while others stay solid
Fractional Crystallization
Just as minerals melt at different rates, they cool at different rates as well
Fractional crystallization is a process where minerals forma at different temperatures
The last minerals to melt are the first minerals to crystallize
Mineral Composition Three main groups of igneous rocks
o Felsic, mafic, intermediate Felsic rocks such as granite are:
light colored, high silica contents, contain quartz and feldspars
Mafic rocks such as gabbro are dark colored, and rich in iron and magnesium
Grain Size Igneous rocks differ in the size of
their grains Grain size is determined by the
cooling rate When lava cools quickly, small grains
form When lava cools slowly, large grains
form
Igneous Rocks as Resources
Very useful for building materials because their interlocking grains make them strong
Also resistant to weathering Granite is commonly used for
building
Ore Deposits Ores are minerals that contain a
useful substance that can be mined at profit
Valuable ore deposits are often associated with igneous intrusions
Ore Deposits: Veins Mineral rich magma fills the cracks
and voids of surrounding rock During magma crystallization, water,
silica and any metals not common in minerals (gold, silver, lead, copper) are left over and eventually solidify to form veins
Ore Deposits: Pegmatites
Vein deposits main contain other valuable resources in addition to metals
Veins of extremely large grained minerals are called pegmatites
Rare elements and crystals are found in pegmatites
Ore Deposits: Kimberlites
Rare, ultramafic rocks that can contain diamonds or other minerals formed only under very high pressures
Formation of Sedimentary Rocks
Sediments are pieces of solid material that have been deposited on Earth’s surface by wind, water, ice, gravity or chemical precipitation
When sediments become cemented together, they form sedimentary rocks
Weathering Weathering is a set of physical and
chemical processes that break rock down
Chemical weathering occurs when rocks are dissolved or chemically changed
Physical weathering occurs when rocks break off but remain chemically unchanged
Erosion and Transport Erosion is the removal and
movement of surface materials from location to another
4 main agents: Wind, moving water, glaciers and gravity
Deposition Deposition occurs when sediments
are laid down on the ground or sink to the bottom of water
Sediments in water will create layers, with large particles settling first
Wind only moves fine sediments Glaciers and landslides move all
sediments equally
Burial Most sediments are deposited in
basins where the building layers increase pressure and temperature
Increasing pressure and temperature cause lithification, or the chemical and physical processes that transform sediments into sedimentary rocks
Lithification Lithification begins with compaction The weight of overlying sediments force
sediments together The temperature in earth's crust are high
enough to cause cementation Cementation occurs when mineral growth
cements sediments together into solid rock
Lithification cont… Two types of
cementation New minerals can
grow between sediment grains
The same mineral grows between the sediment grains
Features of Sedimentary Rocks
The primary feature of sedimentary rocks is horizontal layering called bedding
Bedding with particle sizes that become heavier at the bottom is called graded bedding
Cross-bedding is another type of bedding where layers of inclined sediment move forward across a horizontal surface
Causes of Metamorphism
Meta means change and morphe means forms
During metamorphism, rocks change form while remaining solid
Pressure and temperature increase with depth
Temperature comes from earths internal heat
Pressure comes from overlying rocks or compression during mountain building
Types of Metamorphism
When high temperature and pressure affect large regions of crust, they produce large belts of regional metamorphism
When molten rock come into contact with solid rock, a local effect called contact metamorphism occurs
When very hot water reacts with rocks and alters its chemistry and mineralogy, hydrothermal metamorphism occurso Occurs near igneous intrusions and active
volcanoes
Metamorphic Textures Metamorphic rocks have two textural
groups: foliated and nonfoliated Wavy layers and bands of minerals of flat
crystals characterize foliated metamorphic rockso Schist from shale (clay) and gneiss from
granite
If I said you were gneiss, I’d be for of schist! lol
Metamorphic Textures Cont…
Nonfoliated rocks lack mineral grains with flat crystals and instead have blocky crystal shapeso Quartzite from quartz-rich sandstone and
marble from limestone