1. What are Igneous rocks?
Chapter 5 Section 1

2. Vocabulary Lava Igneous Rocks Partial Melting
Magma that flows out onto Earth’s surface
Igneous Rocks
Rocks that form when lava or magma cools and minerals crystallize
Partial Melting
Some minerals melt at low temperatures while others remain solid
Fractional Crystallization
The first minerals that crystallize from magma are the last minerals that melted during partial melting.

3. Igneous Rock Formation
Heat that melts rocks
Theory
The remaining energy from Earth’s molten formation
Heat generated from decay of radioactive elements

4. Composition of Magma
Type of igneous rock that forms depends on the type of magma
Magma-
A slushy mix of molten rock, dissolved gasses and mineral crystals.
Silica most abundant
Others include:
Oxygen, silicon, aluminum, iron, magnesium, calcium, potassium, sodium

5. Composition of Magma Silica
Greatest effect on magma characteristics
Magma classifications-based on silica amounts
Basaltic
Andesitic
Rhyolitic
Silica content affects melting temperature and how quickly it flows

6. Basaltic Magma Silica content: 42-52% Hawaiian Islands
Freely flowing liquid
Oozes out through cracks in ocean floor or spills out of volcanoes

7. Andesitic Magma Silica content 52-66%
Cascade Mountains, Andes Mountains
Composition between basaltic and rhyolitic
Can produce violent volcanic eruptions

8. Rhyolitic Magma Silica Content more than 66% Yellowstone National Park
Less dense than basalt
Thick, stiff magma
Violent volcanic eruptions

9. Magma Formation Magma forms Four main factors Melting Earth’s crust
Melting within mantle
Four main factors
Temperature
Geothermal gradient- Earth’s temp. increases
Pressure
Increases with depth
Water content
Amount of water present can change the melting point of the rock.
Mineral content

10. Mineral Content
Elements and compounds give magma its overall character.
Melting points of minerals differ
Basalt melts at high temperature
Granite melts at low temperature
Rocks rich in iron and magnesium melt at higher temperatures than rocks containing higher levels of silicon

11. Partial Melting Not all parts of a rock melt at the same temp.
Elements and compounds affect melting temp
Igneous rocks are a combination
Some parts of rock melt at lower temp than others.
If the temp is not high enough to melt the whole rock
Resulting magma will have a different composition than the original rock

12. Bowen’s Reaction Series
N.L. Bowen showed that as magma cools and crystallizes, minerals form in predictable patterns.
Two main branches
Continuous gradual change (feldspar group)
Abrupt change (iron group)

13. Iron Rich Minerals Undergo abrupt changes as magma cools
As the temperature drops enough for a new mineral to be formed
Previously formed minerals react with the magma and new minerals are formed

14. Feldspars Continuous change As magma cools
Earliest formed minerals have high levels of calcium
As they cool farther and react with the magma, they become sodium rich
If cools too quickly, calcium rich minerals do not react completely leaving zoned crystals P. 115

15. Fractional Crystallization