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Geology, Palaeontology & Archaeology / Re: How to genetically classify a weathering mineral?
« on: 19/11/2021 21:58:26 »
I think this is really a matter of semantics, or perhaps language translation?
Supergene processes are simply geologic processes that involve weathering near the surface of the earth- oxidation is the most notable, but enrichment may also be a supergene process. Freedictionary defines supergene processes as "processes of the physical and chemical conversion of mineral matter in the upper parts of the earth’s crust and on its surface through the action of the atmosphere, hydrosphere, and living organisms at low temperatures. They consist in chemical decomposition, solution, hydrolysis, hydration, oxidation, and carbonization"
Most mineral alteration is not caused by supergene processes- much of it is caused by heat, pressure and hydrothermal (hot waters) circulation in the rocks.
The case of bauxite (aluminum ore) is caused by supergene processes: Aluminum does not oxidize easily in surface conditions, so as aluminum rich (especially feldspar rich) rocks chemically weather in the tropics, almost everything besides Fe and Al go into solution and are washed out, leaving a layer enriched in Al.
The case of chrysotile is not caused by supergene processes, and is also not sedimentary. Chrysotile is formed by metamorphism of mafic igneous rocks (mostly oceanic rocks when they get shoved into continents) and is one of main components of serpentine. These rocks form deep underground and eventually are exposed at the surface due to erosion, making chrysotile endogenic, metamorphic.
I applaud you for putting together your classification scheme. I agree that diagenetic minerals (example dolomite) should be classified sedimentary.
I hope this helps- please feel free to contact me about any other minerals.
I think "weathering" is less confusing than "surface alteration", because alteration can be caused by many geologic processes and is not limited to only surface conditions.
Supergene processes are simply geologic processes that involve weathering near the surface of the earth- oxidation is the most notable, but enrichment may also be a supergene process. Freedictionary defines supergene processes as "processes of the physical and chemical conversion of mineral matter in the upper parts of the earth’s crust and on its surface through the action of the atmosphere, hydrosphere, and living organisms at low temperatures. They consist in chemical decomposition, solution, hydrolysis, hydration, oxidation, and carbonization"
Most mineral alteration is not caused by supergene processes- much of it is caused by heat, pressure and hydrothermal (hot waters) circulation in the rocks.
The case of bauxite (aluminum ore) is caused by supergene processes: Aluminum does not oxidize easily in surface conditions, so as aluminum rich (especially feldspar rich) rocks chemically weather in the tropics, almost everything besides Fe and Al go into solution and are washed out, leaving a layer enriched in Al.
The case of chrysotile is not caused by supergene processes, and is also not sedimentary. Chrysotile is formed by metamorphism of mafic igneous rocks (mostly oceanic rocks when they get shoved into continents) and is one of main components of serpentine. These rocks form deep underground and eventually are exposed at the surface due to erosion, making chrysotile endogenic, metamorphic.
I applaud you for putting together your classification scheme. I agree that diagenetic minerals (example dolomite) should be classified sedimentary.
I hope this helps- please feel free to contact me about any other minerals.
I think "weathering" is less confusing than "surface alteration", because alteration can be caused by many geologic processes and is not limited to only surface conditions.