[Chemistry4me]

Some sort of cyanobacteria-like fossil?

[JimBob]

Yep, algal mats, not stromatolites, 3.2 billion years old - found in South Africa

[Bass]

what happened to the 3.4 to 3.5 B cyanobacteria fossils found in the Barberton Greenstone belt in South Africa? 

[JimBob]

They are probably still there. And there is good evidence that they are life forms older than 3.5 years old. This date comes from the greenstone itself and is thus from a metamorphic rock.

But http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1578735

When I ran across this on the BBC web site it was billed as the oldest fossil in existence.

I feel like Eeyore.
Can I take any more?
Thank you, Friend Bass -
You made me an As*

[Chemistry4me]

[Bass]

Take no offense master JBs
I bow before your expertise
As to your poetry, I pass
Cause Eeyore’s already an as*

[frethack]

This should appeal to the chemists as well.

Why do speleothems grow fastest in dryer winter conditions with low rainfall and low CO_{2 (g)} in the cave atmosphere?

Just had a speleo-climatology lecture today...hehehe

[JimBob]

Why should we care???

[frethack]

Why should we care???

Because speleothems are used as proxies for rainfall/climate data!  If they are only recording winter/early spring rainfall then we will surely have to rethink how we use them.

Heres the stoichiometry...maybe that will help?

CaCO₃ + 2H⁺ = Ca²⁺ + H₂O + CO₂(gas)

[JimBob]

Does this mean spelunkers will die of carbon dioxide poisoning?

[Chemistry4me]

Spelunkers? []

[JimBob]

Spelunkers? []

Why yes, C4 It is always useful to have a dictionary around or on yuor computer. Here iss what mine says:

spe-lunk-er (spi lung'kuhr)  n.
                  1.  a person who explores caves, esp. as a
                       hobby.
             [1940-45; < L spelunc (a) cave (< < Gk spêlynx, s.
             spelyng-, akin to spélaion; cf. SPELAEAN) + - ER 1]
   Derived words
             --spe-lunk'ing, n.

frethac tried to explain it to me - the production of CO₂ form plant material during winter inhibits the chemical process he posted and thus somehow causes solubility of the carbonate to be less. - heck I'll get him to post it when he gets home from work. As a lowly student - albeit an excellent one - he needs to have a part time job. I will call him and put us all out of our misery with a decent answer to the poser he posted.

[frethack]

Heres the stoichiometry...maybe that will help?

CaCO₃ + 2H⁺ = Ca²⁺ + H₂O + CO₂(gas)

It would also help to post the correct stoichiometry...sorry guys!  []

Ca⁺²(aq) + 2HCO₃^-(aq) <---> CaCO₃(s) + CO₂(g) + H₂O(l)

The above is the degredation of bicarbonate (a product of carbonic acid) into calcium carbonate.

Biological production during the spring/summer months generally increases soil CO₂, which dissovles into groundwater, forms carbonic acid (and later bicarbonate), and seeps into the cave system.  As excess CO₂ builds up from increasing soil production and limited ventilation of the cave atmosphere the reaction that forms the speleothems (stalactite/stalagmite/helectite etc.) is driven backward, which keeps the bicarbonate in solution and limits speleothem growth.

[maruti.int]

Dear All
           How are you, I have a unique problem for you guys. I have a Sand stone(image is attached), This sand stone is having base colour of yellow. and there are Red and White Veins in between. These white veins are made of Milk Quartz. We want to change the colour of these white veins into red. Please tell us the way to do it.
regards
varun agarwal
 [ Invalid Attachment ]

[Bass]

History of this rock??

 [ Invalid Attachment ]

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[Solius]

A re-worked arenite peeble that has under gone tensional stresses associated with some orogeny???(quartz veins?) Too, some graded bedding indicative of the paleo flow regime in the original environment.

hey, I'm, trying.

[Bass]

Picked this up in NW Montana yesterday whilst waiting for a horse show.  Looked like lots going on for such a small rock - just thought I'd throw it out for discussion.  Exposures in the area are upper Belt Supergroup (Missoula Group).

[Bass]

When I look at this rock, I see mud rip-ups, soft sediment deformation, cross-beds and a graded bedding mix of iron stained mudstone, siltstone and sandstone.  Suggests shallow water deposition with differing energies, slumping and channels.  The rock has been slightly metamorphosed to argillite/siltite/quartzite.  After millions of years of burial, this rock was uplifted and eroded, tumbling down some stream or river to give it a rounded shape.

 

[JimBob]

WHAT A ROCK!! Find another like it - I want one!!!

And dang, Bass, you don't need to team up with a sedimentologist for your work.  Why did you do it?

There looks to be a bit of bio-turbation (see picture below) but it probably isn't, what with it being Mezoproterizoic. Of course you never know what was around 1.6 Billion Years Ago. Aliens? I'll bet it is just a strange looking rip-up clast

Lastly, what struck me about this specimen was is sub-hexagonal shape. That is easily produced by one set of stress, a shear and the two accommodation ax-es. (hyphen for pronunciation - it is the correct plural) The stress regime was perpendicular to the bedding planes. There are also small-scale load cast? visible. 

[Bass]

Don't have another one...

would a nice breccia do?