Rock ID
- Thread starter bagpuss
- Start date
Haematite has a known form ' Botrryoidal' in mineralogy
.Andy Farrant
Active member
Yes, most likely tufa.
Lankyman
Well-known member
Talking of tufa, my mum and I were at the waterfall in Dyserth, North Wales yesterday and there's an impressive amount of it there including the big pillar behind and left in the photo. It's even forming on the handrails of the bridge. I don't know where the water comes from but I was surprised at the flow given how dry it's been.
Cantclimbtom
Well-known member
Intrigued as a non geologist (i.e. a bit ignorant), so I looked up Tufa
webapps.bgs.ac.uk
Tufa is a sedimentary rock composed of calcium carbonate or silica, formed by evaporation as a thin, surficial, soft, spongy, semifriable encrustation around the mouth of springs, seeps or along streams carrying calcium carbonate in solution, and exceptionally as a thick deposit along lake shores. Travertine is a hard, dense variety of tufa; it also occurs in caves as stalactites and stalagmites. Synonyms: sinter, travertine
The first picture look a bit more like big riverbed cobbles with gaps between them - not glued together as an encrustation. So is it Tufa?
Could it be a conglomerate of some kind where the finer softer fill has eroded exposing cobbles?
However in the top pic again there looks like damage and the "cobbles" lost a chunk but in an almost spalling off a layer kind of way, which means it could be some sort of concretions?
Watching the thread with interest...
BGS Lexicon of Named Rock Units - Result Details
webapps.bgs.ac.uk
Tufa is a sedimentary rock composed of calcium carbonate or silica, formed by evaporation as a thin, surficial, soft, spongy, semifriable encrustation around the mouth of springs, seeps or along streams carrying calcium carbonate in solution, and exceptionally as a thick deposit along lake shores. Travertine is a hard, dense variety of tufa; it also occurs in caves as stalactites and stalagmites. Synonyms: sinter, travertine
The first picture look a bit more like big riverbed cobbles with gaps between them - not glued together as an encrustation. So is it Tufa?
Could it be a conglomerate of some kind where the finer softer fill has eroded exposing cobbles?
However in the top pic again there looks like damage and the "cobbles" lost a chunk but in an almost spalling off a layer kind of way, which means it could be some sort of concretions?
Watching the thread with interest...
bagpuss
Well-known member
Spring fed maybe? The ones I've seen fed by emerging underground springs up stream seem to flow fairly strongly still in dry weather.
Andy Farrant
Active member
Tufa forms by the gradual accretion of calcium carbonate, so once it starts to form it can assume various forms including botryoidal spheres, but yes, it can also form around foreign objects such as pebbles creating a tufacous conglomerate. Always best judged in context. You can get similar looking fake rock in some ornamental gardens and grottos, sometimes known as Pulhamite.
The Dyserth falls are on the river that is fed in part by Ffynnon Asaph, which is a karstic spring fed by quite a big catchment with several stream sinks. See https://www.cambriancavingcouncil.org.uk/registry/ccr_registry_view.php?ID=2020-24
The Dyserth falls are on the river that is fed in part by Ffynnon Asaph, which is a karstic spring fed by quite a big catchment with several stream sinks. See https://www.cambriancavingcouncil.org.uk/registry/ccr_registry_view.php?ID=2020-24
Lankyman
Well-known member
There's a level of some sort as well beside the path but I only went in a few metres. There must be a lot of dissolved limestone in the water as it was forming little dams all along the stream out to and beside the road.
Brains
Well-known member
My preferred opinion is tufa. However, some points to consider...
Some of it appears to have a regular surface, like grown against something.
It has an appearance reminiscent of pillow lava, could it be molten industrial waste tipped into water (furnace slag?)
The surrounding area may have an industrial origin that should be considered
While happy with a working theory of tufa, a detailed examination would be needed for a proper ID
Some of it appears to have a regular surface, like grown against something.
It has an appearance reminiscent of pillow lava, could it be molten industrial waste tipped into water (furnace slag?)
The surrounding area may have an industrial origin that should be considered
While happy with a working theory of tufa, a detailed examination would be needed for a proper ID
Similar threads
