UKH

I am not a climber but would like some information about the red/crimson rock surface at Cadshaw please.

If you break open an unexposed surface is it red or does it slowly become red when the air/moisture contacts it ? 

Grateful for any comments.

Many thanks.

My recollection is that the red is some sort of lichenous vegetation that grows on the surface but haven't climbed there for over 15 years so could be wrong.

The lichen growth sounds a very plausible explanation, but I wonder if this is a colourless iron rich deposit normally held within the rock which becomes brow/red (oxidised) when the rock is broken open and exposed to air and moisture. 

I do believe it's iron in the rock. You can find scattered around on grit, Shining Clough is another spot with a very distinct red tint.

British Geological Survey (BGS) publish maps and do geology of UK so take a look in that direction. Most of the rock between Darwen and Bolton fall into a range of Triassic sedimentary: mudstone siltstone sandstone and rocks in the millstone grit group outcropping there (very good for climbing!) such as millstone grit and other related sedimentarys. The red colours are from iron content, once exposed to the air for a while it may darken to a darker red ochre colour but also in drainage water it might be a bit brighter red ochre if the water's more acidic. Definitely Google this adding BGS to get their online mapping etc in your results, then you can see all the nerdy geological detail. Enjoy...

I'm fairly certain the red is from Iron oxide but my guess is the staining is from run-off from above rather than something in the rock itself. Gritstone is made up of particles of sand/gravel eroded from sedimentary rocks (eg granite) so don't (I think) contain much iron. That said you do sometimes get rugosities in grit which I think are iron rich particles. But yeah I reckon it's staining from iron washed out of the soil above.

You get loads of iron rich sediments in sandstone, mudstone/shale areas around the Peak and Pennines.

https://www.bgs.ac.uk/map-viewers/bgs-geology-viewer/

They seem to have discontinued it in mobile app form

As said already the red colour on the surface of the rock is due to the presence of iron. When the sandstone formed the grains of sand were cemented together during lithification (posh name for turning into rock) by various compounds, Calcium Carbonate is a common one as are various oxides of Iron or a combination. The colour changes with oxidation state, in a fresh sample of rock from this bit of the world it is more likely to be a shade of yellow/orange but will over time become darker as it further oxidises. If you see a freshly broken bit you'll maybe see the darker red/brown shade is only in the outer few millimetres of the rock.

The red stuff at Shining Clough is lethal!