1. Ch. 4/5 Notes Day 1
10/26/16

2. Objectives
Students will be able to explain the effect of temperature and cooling rate of magma on the formation of different minerals within igneous rocks

3. Composition of magma
The type of igneous rocks that form depends on the composition of the magma.
The amount of silica that is found in the magma determines the type of rock.
3 types of magma
Basaltic (dark) -42%-52% silica
Andesitic (medium) – 53%- 66% silica
Rhyolitic (light)–more than 66% silica

4. Magma formation There are 4 main factors involved in magma formation:
Temperature- increases with depth
Pressure- increases with depth. Results in increased melting temperatures.
Water content- changes the melting pt of magma. Increase water = decreased melting pt.
Mineral content – In depth on the next page.

5. Igneous rocks from magma
Igneous rocks form when molten rock, magma, cools & solidifies.
This molten rock originates in the Aesthenosphere, through cracks in the lithosphere 200 kilometers within the earth.
The magma consists largely of elements found in silicate minerals, gasses and water vapor.
Because the magma is lighter then surrounding rock it makes it's way to the surface.

6. The Rock Cycle

7. But First, What is a Rock? Rock – consolidated mineral matter
So what’s a mineral?
Mineral – naturally occurring, solid, inorganic elements and compounds that form crystals
Where do minerals come from?
The core of the earth is like a big magma soup of different elements all floating around in solution
This hot magma rises and begins to cool. As it cools, the elements in the solution begin to bond and form minerals. THE TYPE OF MINERAL FORMED IS DETERMINED BY THE KIND OF ELEMENTS IN THE SOUP AND HOW FAST OR SLOW THE MAGMA COOLS

8. More on Minerals
A mineral is any naturally occurring inorganic solid that possesses an orderly internal structure and a definite chemical composition.
Properties of Minerals
naturally occurring (not made by humans).
inorganic (teeth, seashells, trees, etc. are excluded)
solid (not a gas or a liquid)
orderly internal structure
definite chemical composition
Examples: C Diamond
NaCl Halite
(Na,Ca)Al(Si,Al)Si2O8 Plagioclase

9. Mineral Content change In Depth
Different minerals form and/or melt at different temperatures and pressures
The way minerals form and melt are described by the following three processes:
Fractional Crystallization
Partial Melting
Bowen’s Reaction Series

10. Partial Melting
The process of some minerals melting while others remain solid as magma temperature increases.
Think about chocolate chip ice cream melting. The vanilla ice cream melts, but the chocolate chips remain solid.

11. Fractional crystallization
The process of minerals crystallizing as magma cools, and are thereby removed from the magma itself.
As hot magma cools, minerals that are low in silica form first (because they form at hotter temperatures) and are no longer part of the magma “soup.”
As these minerals form, the leftover magma will end up having more silica in it.

12. Bowen’s Reaction Series
A chart that describes what minerals form at what temperatures within magma
Based on partial melting and fractional crystallization
Bowen discovered that minerals form in two distinct ways based on their composition
Discontinuous (Left side) – minerals rich in iron and magnesium.
Order (Hot to Cold)- Olivine, pyroxene, amphibole, biotite mica
Continuous (Right Side)– Plagioclase Feldspar formation
Order (Hot to Cold)- Calcium-rich feldspars to sodium-rich feldspars
BOTH SIDES CRYSTALLIZE AT THE SAME TIME

13. Bowen’s Reaction Series
Iron and Magnesium Rich

14. Crystallization Videos
Fractional Crystallization
Crystals Forming From Solution
Bismuth Crystals Forming