by neufer » Tue Jan 19, 2010 4:20 pm
Yeudas wrote:I don't think that the black sand is the one that felt in cascade.
If you look to this picture of dust evil trails, you can see that actually the black sand appears when the pink and clear sand is removed:
http://apod.nasa.gov/apod/ap091021.html
So the upper level of clear sand should be the one that flowed when ice melted.
How is explained the fact that only a thin layer of light sand covers everywhere the darker level?
Is it a phenomena of oxidization?
I would guess that after dust storms the light sand (light in both color & weight)
is the last to "rain out" and physically deposit on an iron heavy hematite surface.
Warm gaseous explosions redeposit the dark hematite onto the surface
http://en.wikipedia.org/wiki/Hematite wrote:
<<Hematite is the mineral form of iron(III) oxide (Fe
2O
3), one of several iron oxides. Hematite is a mineral, colored black to steel or silver-gray, brown to reddish brown, or red. It is mined as the main ore of iron. While the forms of hematite vary, they all have a rust-red streak. Hematite is harder than pure iron, but much more brittle.
Huge deposits of hematite are found in banded iron formations. Grey hematite is typically found in places where there has been standing water or mineral hot springs, such as those in Yellowstone National Park in the United States. The mineral can precipitate out of water and collect in layers at the bottom of a lake, spring, or other standing water. Hematite can also occur without water, however, usually as the result of volcanic activity. Clay-sized hematite crystals can also occur as a secondary mineral formed by weathering processes in soil, and along with other iron oxides or oxyhydroxides such as goethite, is responsible for the red color of many tropical, ancient, or otherwise highly weathered soils.
The spectral signature of hematite was seen on the planet Mars by the infrared spectrometer on the NASA Mars Global Surveyor ("MGS") and 2001 Mars Odyssey spacecraft in orbit around Mars. The mineral was seen in abundance at two sites on the planet, the Terra Meridiani site, near the Martian equator at 0° longitude, and the second site Aram Chaos near the Valles Marineris. Several other sites also showed hematite, e.g., Aureum Chaos. Because terrestrial hematite is typically a mineral formed in aqueous environments, or by aqueous alteration, this detection was scientifically interesting enough that the second of the two Mars Exploration Rovers was targeted to a site in the Terra Meridiani region designated Meridiani Planum. In-situ investigations by the Opportunity rover showed a significant amount of hematite, much of it in the form of small spherules that were informally named "blueberries" by the science team. Analysis indicates that these spherules are apparently concretions formed from a water solution.>>
http://en.wikipedia.org/wiki/Heavy_mineral_sands_ore_deposits wrote:
<<Heavy mineral sands are a class of ore deposit which is an important source of zirconium, titanium, thorium, tungsten, rare earth elements, the industrial minerals diamond, sapphire, garnet, and occasionally precious metals or gemstones. Heavy mineral sands are placer deposits formed most usually in beach environments by concentration due to the specific gravity of the mineral grains. It is equally likely that some concentrations of heavy minerals exist within streambeds, but most are of a low grade and are relatively small. Specific trap sites for heavy mineral sand placer deposits are in beaches on the leeward side of headlands, as this forms a low-energy zone which traps sediments carried along by the longshore drift. Also, sand bars developed at the mouths of rivers which feed the placer deposits are rich trap sites where the winnowing action of the waves are most efficient, because heavy minerals, if they are going to be too heavy to be moved, will deposit at an isthmus in preference to drifting too far down the beach.>>
[quote="Yeudas"]I don't think that the black sand is the one that felt in cascade.
If you look to this picture of dust evil trails, you can see that actually the black sand appears when the pink and clear sand is removed:
[url]http://apod.nasa.gov/apod/ap091021.html[/url]
So the upper level of clear sand should be the one that flowed when ice melted.
How is explained the fact that only a thin layer of light sand covers everywhere the darker level?
Is it a phenomena of oxidization?[/quote]
I would guess that after dust storms the light sand (light in both color & weight)
is the last to "rain out" and physically deposit on an iron heavy hematite surface.
Warm gaseous explosions redeposit the dark hematite onto the surface
[quote=" http://en.wikipedia.org/wiki/Hematite"]
<<Hematite is the mineral form of iron(III) oxide (Fe[sub]2[/sub]O[sub]3[/sub]), one of several iron oxides. Hematite is a mineral, colored black to steel or silver-gray, brown to reddish brown, or red. It is mined as the main ore of iron. While the forms of hematite vary, they all have a rust-red streak. Hematite is harder than pure iron, but much more brittle.
Huge deposits of hematite are found in banded iron formations. Grey hematite is typically found in places where there has been standing water or mineral hot springs, such as those in Yellowstone National Park in the United States. The mineral can precipitate out of water and collect in layers at the bottom of a lake, spring, or other standing water. Hematite can also occur without water, however, usually as the result of volcanic activity. Clay-sized hematite crystals can also occur as a secondary mineral formed by weathering processes in soil, and along with other iron oxides or oxyhydroxides such as goethite, is responsible for the red color of many tropical, ancient, or otherwise highly weathered soils.
The spectral signature of hematite was seen on the planet Mars by the infrared spectrometer on the NASA Mars Global Surveyor ("MGS") and 2001 Mars Odyssey spacecraft in orbit around Mars. The mineral was seen in abundance at two sites on the planet, the Terra Meridiani site, near the Martian equator at 0° longitude, and the second site Aram Chaos near the Valles Marineris. Several other sites also showed hematite, e.g., Aureum Chaos. Because terrestrial hematite is typically a mineral formed in aqueous environments, or by aqueous alteration, this detection was scientifically interesting enough that the second of the two Mars Exploration Rovers was targeted to a site in the Terra Meridiani region designated Meridiani Planum. In-situ investigations by the Opportunity rover showed a significant amount of hematite, much of it in the form of small spherules that were informally named "blueberries" by the science team. Analysis indicates that these spherules are apparently concretions formed from a water solution.>>[/quote]
[quote=" http://en.wikipedia.org/wiki/Heavy_mineral_sands_ore_deposits"]
<<Heavy mineral sands are a class of ore deposit which is an important source of zirconium, titanium, thorium, tungsten, rare earth elements, the industrial minerals diamond, sapphire, garnet, and occasionally precious metals or gemstones. Heavy mineral sands are placer deposits formed most usually in beach environments by concentration due to the specific gravity of the mineral grains. It is equally likely that some concentrations of heavy minerals exist within streambeds, but most are of a low grade and are relatively small. Specific trap sites for heavy mineral sand placer deposits are in beaches on the leeward side of headlands, as this forms a low-energy zone which traps sediments carried along by the longshore drift. Also, sand bars developed at the mouths of rivers which feed the placer deposits are rich trap sites where the winnowing action of the waves are most efficient, because heavy minerals, if they are going to be too heavy to be moved, will deposit at an isthmus in preference to drifting too far down the beach.>>[/quote]