Topic 9: Minerals, Geochemistry, and Weathering Flashcards
What is a mineral?
A mineral is a naturally occuring crystalline solid with a definite, but not necessarily fixed, chemical composition.
They can be produced by abiotic or biotic chemical reactions but it is inorganic in composition.
What features of minerals that can change over geologic time?
- The diversity of minerals
- The relative abundance of specific minerals
- The range of elemental composition of minerals
- The shapes that minerals take
What drove the diversification of minerals on Earth?
- The progressive separation and concentration of chemical elements from their original uniform distribution
- An increase in the range of variables (different elements) that control which minerals form
- The generation of far-from-equilibrium conditions by living systems (eg. Great Oxygenate Event, or era of biologically mediated mineralogy). A change in living conditions affect the diversification of minerals.
What can we imply from a mineral name and how are those factors related to the minerals themselves?
A mineral name implies that the mineral has:
- A definite elemental composition
- A crystal structure: an ordered and “infinitely” repeating arrangement of atoms
==> Determine the properties of mineral
When will a mineral start reacting?
A mineral out of equilibrium in temperature, pressure, and composition of its formation will react.
What are some implications of minerals and why is that?
Minerals act as a record of geological processes or interactions and the composition of the Earth over geologic time. They are also indicators of environmental conditions and also the conditions in which they are formed.
This is because minerals are produced during interactions between the lithosphere, atmosphere, hydrosphere, and biosphere. They also can be long-lasting in the Earth’s crust.
Describe neutralisation and redox reaction
- Neutralisation reaction is a reaction between a base and an acid to produce water and a salt
- Redox reaction involves oxidation and reduction or the transfer of electrons between chemical species
What causes mine drainage acid?
Interaction of sulfide minerals (like pyrite) from acid sulphate soils with water and oxygen creates oxidation reaction and produces a strong acid and metalliferous drainage.
What is weathering and what is is driven by?
Weathering is physical and chemical alteration of rocks and their mineralogical components at the interface between a planet’s crust and atmosphere.
Weathering is driven by interactions between the crytalline Earth, the atmosphere, the hydrosphere, and life (biosphere).
At what level does weathering occur?
Weathering occurs at sub-micron, molecular, and mineralogical or rock level.
Describe the role of weathering in the rock cycle
Weathering is essential for the formation of sediments from different types of rocks which then turn into sedimentary rocks.
Also, weathering helps in the production of many dissolved components used for making up minerals or participating in biogeochemical cycles.
Identify and describe different types of physical weathering
Physical or “mechanical” weathering involves the disintegration of rock without mineralogical transformation - no chemical change.
- Rock-on-rock abrasion by wind, water, and ice
+ Knock against each other
+ Break off at the corners ==> kinda round - Thermal expansion/contraction:
+ Rocks have different minerals within which reacts differently in different temprature ==> contract, expand constantly
+ Shatter or broken down (usually in places in changing or extreme temperature) - Pressure release:
eg. igneous intrusions like batholith is overlain by kms of soil/other types of rocks
+ Over time, the rock is weathered away by erosion
+ Release of pressure, uplift and cooling of the batholith –> pressure expansion –> rise to surface and create sheets joints or the shearing away of the rock surfaces - Crystallisation pressure:
+ Ingress of water or components in water into fractures or pores of rocks
+ React with the rocks, creating new, more expansive minerals which take up more space and then, shatter the original rock
+ Salt weathering: ingress of ions as sea water hitting the rocks - Biomechanical process: life like tree roots develop in between the rock fractures
+ Humans pulverise rocks to extract resources
Identify and describe different types of chemical weathering
Chemical weathering involves transformation in mineralogical features of the rocks or a change in elemental composition and crystal structure of naturally occurring chemical compounds.
- Dissolution in water (hydrolysis)
- Dissolution mediated by acids (organic or inorganic)
- Oxidation/reduction (can be catalysed by microbes)
- Dehydration/hydration
- Mediated by biological processes (biochemical weathering)
eg. lichen secreting acids on rocks –> attack rock surface –> break down the components of rocks to extract energy
Identify and describe some major factors that control the rate of chemical weathering
- Temprature (higher temperature, higher reacting rate)
- Surface area exposed available to react with water, air, and accessible to organisms
- Composition of solutions to which minerals are exposed (pH, ions, oxygen, etc.)
- Strength of the chemical bonding in a mineral’s crystal structure
