Opportunity finds a new type of rock, sol 886 Microscopic Imager near Beagle crater Options

[Guest_Richard Trigaux_*]

On sol 886 Oppy's microscopic imager takes shots of a new type of stone previously unseen in Meridiani planum. This place was already shot on sol 885 by the Panoramic Camera, showing a patch of soil looking like gravel.


These stones are clear, chalky looking, with angulous fractures, but slighty rounded as if transported for a while in a river bed. They also show some hollows or veins in some places. In the background there are small more or less rounded stones evoking the smaller blueberries already seen in the beginning.


So I wonder what these stones could be. The most conservative explanation would be that they are freshly broken jarosite, submitted to a bit of eolian erosion. But other explanations are possible. We shall remain in the expectative until some analysis is done.

[dvandorn]

The rock in question, in the MI images, looks like it has microclasts. It seems to have more than one type of material in it, and yet it all seems to be about equally resistant to erosion.

I think, quite possibly, what we have here is a pebble ground out of a piece of impact melt. Such melt often contains microclasts of material swept up with the melt sheet.

Now, whether it's melt from the Victoria impact, or the Beagle impact, or even a farther-reaching impact, this is the kind of thing I'd expect to see in impact melts on Mars.

-the other Doug

[Guest_Richard Trigaux_*]

Inpact melt?

I don't think that jarosite can melt, it would rather change of chemical composition, from a sulphate to an oxyd (a common industry process). Which could, after, melt...

[imipak]

I don't think that jarosite can melt, it would rather change of chemical composition, from a sulphate to an oxyd (a common industry process). Which could, after, melt...

Oxide? But where would the oxygen atoms come from? Hmmm, I suppose if it was an aqueous environment...

It's an interesting question though - what, chemically speaking, would happen to evaporite subjected to a brief blip of intense heat and pressure?

[Guest_Richard Trigaux_*]

Oxide? But where would the oxygen atoms come from? Hmmm, I suppose if it was an aqueous environment...

It's an interesting question though - what, chemically speaking, would happen to evaporite subjected to a brief blip of intense heat and pressure?

No problem, the oxygen is already in there. Sulphates are compositions of the sulphate ion SO4-- with one or two metallic ions (2x M+ or M++) together with water molecules which are required to make the sulphate crystal as we find it.

When heated, (about 100°C??) usualy a sulphate first lose its crystalisation water. It is what happens when industry does plaster from gypsum.

When heated more, (about 200°C??) the sulphate ion breaks, releasing SO2. The remaining oxygen is now available to combine with the metal, it cannot do otherwise anyway because it is already reduced so it cannot escape the combinaison with the metal ion.


If we heat still more, the oxyde melts, a its own temperature, whic can vary from hundred to thousands degrees.




What happens to shocket sulphates? probably what happen to other crystals. I found an interesting link to this about heating asteroids (alternate PDF file). They explain that crystals submitted to intense shock waves undergo a variety of transformations: irregular fractures and melt pockets, together with a heating increasing with the intensity of the shock wave. For low intensities, the effect would not be very different with jarosite, but when we come to higher temperatures, the effect must be different, as jarosite cannot melt without undergoing a chemical change, involving emission of gasses.

[tty]

No problem, the oxygen is already in there. Sulphates are compositions of the sulphate ion SO4-- with one or two metallic ions (2x M+ or M++) together with water molecules which are required to make the sulphate crystal as we find it.

When heated, (about 100°C??) usualy a sulphate first lose its crystalisation water. It is what happens when industry does plaster from gypsum.

When heated more, (about 200°C??) the sulphate ion breaks, releasing SO2. The remaining oxygen is now available to combine with the metal, it cannot do otherwise anyway because it is already reduced so it cannot escape the combinaison with the metal ion.
If we heat still more, the oxyde melts, a its own temperature, whic can vary from hundred to thousands degrees.

There has been a lot of work done on this subject in connection with the Chicxulub impact which occurred in carbonate/sulphate rock and it is well established that very large amounts of SO2/SO3 and CO2 were liberated. There is little doubt that the CO2 remained in the atmosphere for a fairly long time (millenia), while there is more doubt about the sulfur. Sulfuric acid from volcanboes remains in the stratosphere for a few years, but some people think that the sulfuric acid from Chicxulub would quickly have reacted with other material (dust) in the ejecta and fallen back to Earth. Of course things might work differently in the very thin and dry Martian atmosphere.

tty

[Guest_Richard Trigaux_*]

There has been a lot of work done on this subject in connection with the Chicxulub impact which occurred in carbonate/sulphate rock and it is well established that very large amounts of SO2/SO3 and CO2 were liberated. There is little doubt that the CO2 remained in the atmosphere for a fairly long time (millenia), while there is more doubt about the sulfur. Sulfuric acid from volcanboes remains in the stratosphere for a few years, but some people think that the sulfuric acid from Chicxulub would quickly have reacted with other material (dust) in the ejecta and fallen back to Earth. Of course things might work differently in the very thin and dry Martian atmosphere.

tty

Errr? what I heard until recently was that Chicxulub impact punched throught two cristaline (granite-like) layers (which were dated with uranium clock) and that the limestones layers were deposed on it afterward, giving a flat surface obliterating the crater. So that there would be no carbonates involved.

On the other hand, the Ries crater in Germany made into a granite layer, covered by some tens of metres of limestone and shale deposits. There is a work about the granite melt, which gave a layer of about 10m of lava spread all over the crater rim, and nice glass-like light green tectites known as moldavites (because they were found in Moldavia). I know the limestone-shale layers formed large blocks (several hundred metres) which were lifted and then fell back on the crater bottom, sometimes turned upside down, but still with the layering recognizable (shattered I imagine). But I don't know how they responded to shock and heat. We can imagine that shale and clay can form a lava too, we can even try to melt some. Some carbonates too can exist in a liquid form. But sulphates, I don't know.