Historical Geology 102
Minerals and Rocks
What is a Mineral?
Mineral Physical Properties
Physical aspects of a mineral, based on chemical composition and crystalline structure.
Other - Specific Gravity, Magnetism, Taste, Hydrochloric acid - HCl, Radioactivity, Fluorescence
Important Crustal Minerals
Feldspar Group (Plagioclase and Orthoclase)
Calcite and Dolomite
Pyroxene Group (Augite)
Amphibole Group (Hornblende)
Mica Group (Biotite and Muscovite)
Halite - "Salt"
Additional information and images on Igneous Rocks can be found at: Minerals
The Rock Cycle
Rocks that formed from the cooling and crystallization of magma
Origin of Magma
Magma - liquid rock or molten rock
Things needed to make magma:
Material to be melted - any pre-existing rock (crustal material) - mantle material
Increased temperature will cause melting
Sources of heat in the Earth's interior
Thermal gradient - temperature increase with depth - ~30°C per kilometer
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:
Decrease in temperature (cooling)
Partial melting says that different material melt at different temperatures
Different materials solidify or crystallize at different temperatures
Additional information and images on Igneous Rocks can be found at: Igneous Rocks
Additional information and images on Volcanic Rocks can be found at: Volcanic Rocks
Additional information and images on Volcanoes can be found at: Volcanoes
Rocks formed from:
Sediment - fragments of pre-existing rocks or minerals, biologic organisms or chemical precipitates
Additional information and images can be found at: Sedimentary Rocks
The Sedimentary Cycle
Metamorphic rocks are rocks which have undergone a change of form.
Parent Rock is the original, unaltered, unchanged rock.
Parent rocks can be igneous, sedimentary or metamorphic rocks.
Metamorphism occurs due to changes in temperature, pressure or chemistry.
Temperature and Metamorphism
Changes in temperature will result in changes to the minerals or structure of the rock.
The temperature of metamorphism has two limits:
Lower limit of metamorphism - 200°C
Upper limit varies between 700-1200°C
What is the ultimate temperature of metamorphism?
Pressure and Metamorphism
Changes in pressure will change the crystalline structure of minerals and the structure of the rock.
Hydrothermal fluid is hot water, plus other chemicals and gases.
1) remove chemicals from the rock
2) add chemicals to a rock
A change in chemistry will result in new minerals.
Change the minerals and the rock also changes.
Types of Metamorphism
Additional information and images about Metamorphic Rocks can be found at: Metamorphic Rocks