IGNEOUS ROCKS

Igneous Rocks Form from the crystallization of magma

From Latin “ignis” which means fire Most common rocks in the Earths crust by

far Two types of Igneous Rock

Extrusive Cools quickly on the Earth’s surface Fine-grained Evidence

We can actually watch extrusive igneous rocks from as lava cools

Intrusive Cools slowly beneath the surface of the

Earth Coarse-grained (large/rough) Evidence

Cross-cutting relationship with other rock formations

Cross-cutting Most igneous intrusive rocks have cross-

cut something Magma comes up through cracks in

rocks Magma the cools leaving an igneous

intrusion Granite is the most common intrusive

igneous rock

Magma Not a pure substance

Usually contains Molten rock Gases Mineral crystals

Contains the same elements found in the Earth’s crust

Most abundant compound is Silica (SiO4) Found in almost all rocks

Melting Not all parts of magma melt at the same

time This concept is called partial melting

Crystallization Not all parts of magma crystallize

(harden) at the same time This concept is called fractional

crystallization Harder substances (diamonds) harden at

the same time and are harder to melt Pressure causes substances to have

different melting points

Bowen’s Reaction Series Shows the relationship between cooling

magma and mineral formation

Mineral composition Again silica is the primary component of

magma Felsic rocks contain high levels of silica

Resistant to flow Granite, Obsidian

Mafic rocks contain low levels of silica “watery stew” Gabbro, Basalt

Uses Interlocking grain textures make them

very strong They are also highly resistant to

weathering These characteristics make Igneous

rocks excellent building materials.

SEDIMENTARY ROCKS

Sedimentary Rocks Composed of small pieces of rocks that

have been broken down and deposited Wind, water, and other forces transport

sediments to sedimentary basins which can be more than 8 km thick.

Clastic sediments Boulder > 256 mm Cobble 256 - 64 mm Pebble 64 - 2 mm Sand 2 – 0.062 mm Silt 0.062 – 0.0039 mm Clay < 0.0039 mm

Buried Sediments experience high pressure and temperature

This causes lithification, which is the process of sediments turning into rock

Sedimentary rocks can also form from cementation Sediments are cemented together by

mineral growth

Sedimentary Uses Evidence of past events and life

Due to the presence of fossils Energy sources

Oil Natural gas Coal

METAMORPHIC ROCKS

Metamorphic Rocks From the Greek “meta” meaning change,

and “morphe” meaning form Rock is buried and experiences great

pressure and temperature, but doesn’t quite melt Very common in “mountain-building” areas

During metamorphism, rocks change form while remaining solid

Types of metamorphic rock Foliated

Minerals with flat needle-like structures line up in wavy layers and bands

Non-foliated Mineral grains lack the flattened structure

Rock Cycle The remaking of rocks