Concretions need a porous / permiable rock for water flow, but concretions do not need a void to fill. Typically, there is a small grain of Fe mineral (pyrite, magnetite, hematite) which in the presence of intersticial water diffuses spherically outward, cementing the matric with new minerals. With jarosite, I think the original grains could have been pyrite, or even chalcopyrite. Remember that one half sphere with the dark center and concentric zoning? The Dakota sandstone on the ridge behind our house has abundant concretions. It is a very porus rock, but no real voids. Neat concretions though, lots of funny shapes that weather out.
The tabular crystal could be soft enough for aeolean differential weathering on the surface. not sure that is a clear call for water.
Sulfates are not primary (igneous) minerals, they need an aqueous enviroment. Also, the sulfates in question need potassium feldspar as a precurser, which is not a mafic (ie basalt) mineral. The other thing 'bout jarosite, when it forms in the weathering of ore deposits, is that a by-product is Bornite, a copper-iron sulfide that is purple-blue. Intersting.
I think Nick's sabka or evaporites are good models at this point.
Space/Science » in reply to We should be careful that the evidence so far is conclusive of ground water not surface water
voids not needed for concretions
The whole thread (40 posts)
- "liquid water once drenched the surface" (Opportunity site). WOW! LIVENASATV news announcements on now folks. (n/t)
- A virtual toast with my bottle of Perrier :-)
- re: Samples
- We should be careful that the evidence so far is conclusive of ground water not surface water
- About Jarosite
- If It Looks Like A Duckand and Wobbles Like A Duck
- When Squyres said; Opportunity's landing was a hole in one, he wasn't kidding. Cheers to this outstanding MER mission (n/t)
- Thank God for the internet connection to NASA TV
- You beat me to it.... (n/t)