Mineral Genesis Flashcards
Mineral Genesis
Refers to primary crystallization and post crystallization history of minerals.
Sources of Water
1) hydrothermal processes or at surface as brines
2) crystallizing magma
3) dehydration or decarbonation during metamorphism.
4) meteoric water
5) seawater circulation at MOR
Hydrothermal
Quartz is most important hydrothermal mineral.
In hydrothermal solutions, components are transferred predominately as aqueous complexes.
Gas
Some minerals percipitate directly from the gas state.
ex: Hematite, realgar, native sulfur
Magma
Has properties of a liquid as well as solution.
Anions dissolved in magmas.
Groups locally organized into clusters without long range atomic order.
Polymorphic Reactions
Example: C (diamond to graphite)
FeS2 (Pyrite to marcasite)
CaCO3 (calcite to aragonite)
Pseudomorphs
Example: limonite replacing pyrite
Replacement
Initially nucleus grows, minerals incorporated, and rotation/deformation occurs.
After deformation stops, new mineral continues to grow, replacing original mineral.
Example: Porphyroblasts of garnet.
Mineral Crystallization
Minerals crystallize from pre-existing phases because they are more stable than melts/solutions/pre-existing minerals.
Free Space Crystallization
Usually displays euhedral habit.
Metasomatism Crystallization
Simultaneous dissolution and crystallization; new mineral completely of partially replaces an initial mineral.
Recrystallization
New crystals replace those formed earlier.
Crystal Growth Rates
Extrapolated times that would be required to grow to 1cm in size
Multistage process
Mineralization represents a long-term multistage process.
Crystallization reflects changes in P, T, and chemical composition of environment.
Crystallization can be interrupted by recess, dissolution, and precipitation of other minerals.
Generations
Assemblages of crystals of the same mineral that formed at different times.
