Physical Geology 101
Rocks that formed from the cooling and crystallization of magma
Origin of Magma
Magma - liquid or molten material
Needed to make magma:
Increased temperature will cause melting
Heat is kinetic energy
Heat in an object is related to how fast the atoms are moving in that object
faster motion = higher temperature
slower motion = lower temperature
Atoms in a solid rock are vibrating but not enough to break away from the other atoms
As the temperature goes up, what happens to the atoms?
Sources of heat in the Earth's interior: ?
Increases in pressure will increase temperature.
Increased pressure means higher melting temperature.
How can changes in pressure lead to melting?
Products given off by material as a vapor or gas
Water and carbon dioxide
Volatiles will lower the melting temperature.
Different materials melt a different temperatures.
Partial melting is the melting of some of the material in a rock but not the entire rock.
The composition of a magma will be different from the composition of the rock if the rock is not completely melted.
Reversal of melting resulting from:
Sequence of Crystallization
Partial melting says that different material melt at different temperatures
Different materials solidify or crystallize at different temperatures
Bowens Reaction Series describes the crystallization sequence of common minerals found in igneous rocks
Classification of Igneous Rocks
Two main divisions:
1) Plutonic (Intrusive) Igneous rocks
2) Volcanic (Extrusive) Igneous rocks
Magma cools beneath the surface
Cools slowly - results in large, visible crystals
Phaneritic texture - individual crystals are visible to the naked eye; the entire rock is composed of crystals
Pegmatitic - extremely large crystals (>2-3 cm)
Magma reaches and cools on the surface
Cools rapidly - results in very small crystals or no crystals
Aphanitic Texture - no crystals are visible
Porphyritic Texture - some crystals are visible
Glassy - looks like a chunk of glass
Frothy - full of small bubbles
Scoriaceous - lots of bubbles but fewer than frothy
Pyroclastic - fragments of lava
Primarily based on SiO4 content
Mafic - Fe, Mg, Ca, rich - SiO4 poor - tend to be dark to black in color
Intermediate - compositions between mafic and felsic
Felsic - K, Na rich - SiO4 rich - tend to be light colors
Igneous Rocks Identification