The Rock cycle: Initially proposed by James Hutton.

Rocks are grouped into three main families based on their origin

1. Igneous
2. Sedimentary 
3. Metamorphic.

1. IGNEOUS ROCKS:

(Latin:Fire) Formed from the cooling & crystallization of magma (below the surface) or lava (above the surface). (ie melted material)

2. Sedimentary Rocks

Made of sediment

Sediment comes from the weathering or break up of other rocks, primarily igneous rocks.

Erosion is the breakup and transport of the sediments to different locations.

3. Metamorphic rocks

Heat and pressure applied to the sedimentary and igneous rocks results in the recrystalization of new minerals with different physical properties.

With enough heat the rock melts to form and igneous rock completing the rock cycle.

Naming of Igneous rocks

Classified according to:

1. Texture (Size of the crystal grains) 

2. Mineral composition (What is the rock made of.)

1. Texture Terms:

Aphanitic: (Microcrystalline) Mineral grains are too small to be seen. (Usually volcanic)

Phaneritic: (Coarse grained) Mineral grains can be easily seen.(Usually plutonic)

Porphyritic: Large crystals embedded in a matrix of smaller crystals.

Fine-grained Texture: Volcanic

formed at surface

from lava

Coarse-grained texture: Plutonic

formed at depth

from magma

Porphyritic Texture:

Phenocrysts: Large crystals in a Matrix or Ground mass of smaller crystals.

Other types of textures:

Glassy: too fast to form minerals

Composition terms:

Mafic: (Magnesium and Iron rich) Darker and heavier minerals. Low in silica. They are the first minerals to harden from a magma.

Felsic: (Feldspar and silica rich) Lighter in color and density.

Naming Igneous Rocks: (See handout)

Describe the processes that change the composition of magma

Bowen’s Reaction Series

minerals crystallize at diff. temps

mafic crystallize at hotter temps

felsic at cooler

Differentiation

Cooling magma

mafic crystals first

settle to bottom

rest of magma becomes more felsic

Note felsic at bottom, mafic at top

Assimilation: as magma rises incorporates surrounding rock