UKC

I presume its some sort of lichen?

Anyone on here know about this?

cheers

Mark

In reply to Pylon King Against Capit@lism:

I don't know, but suspect it's something intrinsic to the rock rather than a surface coating of lichen as water-streaks on limestone are usually black and what's more the rock is usually extremely hard and sound. In the Dollies you can to a certain extent judge rock quality by colour, with a sequence (from bomber to choss) of black>grey>white>yellow>red. I don't know if calcium carbonate can become hydrated? - hopefully a geologist can give the full picture.

Rick

In reply to Pylon King Against Capit@lism:

I wouldnt call myself an expert on the area, but from what I remember im pretty sure its to do with the various compounds in the rock and how they react with water/air. And also in the way they were originally deposited. More clay/silt gives a yellowy brown colour, but if lots of organic compounds are present its greener, or bluey. And red is to do with oxidation of iron compunds (predictably!) I think black limestone can also occur when it heats up significantly.
Of course this doesnt answer the question of why quarried limestone specifically is turning black!

In reply to james.slater:

I always believed it was to do with the seepage of trapped organic carbon from the fossilised organics. On natural limestone it has been seeping out for thousands of years so there is little left in the rock. On quarried stuff the surface is relatively new and there is still a lot of carbon trapped in the rock just behind the surface, which is trying to seep out relatively quickly.
Not brilliantly explained, but you get the idea.
Ashford black marble is limestone heavily impregnated with organic carbon, I am told.

In reply to johncook:

Thats great thanks.

Do you know what the process is called?

In reply to Pylon King Against Capit@lism:

I've seen the same phenomium on the light yellow sandstone of the Drakensberg in South Africa, where the undersdes of overhangs in particular go black I had always assumed it had something to do with water, but unlike limestone, sandstone isn't soluble in water, or is it?

In reply to Pylon King Against Capit@lism:

I think the grey colour is algae/lichen growing on the surface of the rock. Where rain doesn't reach and these can't survive the natural white of the rock shows through: http://www.stacey.peak-media.co.uk/yorkshiredales/YorshireDales2006/MalhamC...


Chris

In reply to Chris Craggs:

Hmm, so.....what is it?

Lichen or oxidation?

In reply to Pylon King Against Capit@lism:

Limestone in buildings and pavements are prone to a dark discolouration known as "halo staining", which is generally accepted as arising from repeated wetting and drying cycles where the water is alkaline. I don't know if the dark staining on quarried limestone is related.

In reply to Pylon King Against Capit@lism:

I know, I know !

If it's slab then it's got to be wall with easy routes, and thousands of the begginers climbing there, slipping and sliding down while trying routes and leaving delicate layer of decathlon's climbing shoes rubber :p that's why wall turns black !

In reply to Pylon King Against Capit@lism:

or bacteria?
http://en.wikipedia.org/wiki/Gloeocapsa_magma

In reply to malk:
I'll get me microscope out. Test the pollock pink spots at the same time.