Floating Hematite?

Hi all,

A couple of months ago I was on a geology walk in Upper Teesdale. The guy conducting the walk told me that the colourful iridescent films often seen in moorland puddles was neither diesel/oil pollution, nor organic oils from decaying peat (as I thought). He said it was hematite.

Yesterday I took the following photos. Note that the interference colours flow to start with, then break up into rafts, which an oil would not do. I guess the thickness would be in the order of a few angstroms. Had a quick look on the internet, and microbiology is suggested - here & here

Anyone know anything about this?

Regards,
Rog

Hello Roger,
my guess is Schwertmannite.

Cheers,
Pedro Alves

This reminds me of an experiment physicists often do to find the approximate size of an oil molecule. You place one drop of oil on water and it is supposed to spread out in a perfect circle until it is a layer thick. It is the electrostatic interactions between the particles between themselves and the particles and the water that influence whether the film has smooth edges or rough edges (like the "rafts" in your pictures).

In the past when I tried the demo the students spread lycomium powder (small moss spores) on top of the water before the oil drop was placed and it made patterns like the ones in your pictures; The oil slick broke up into rafts just like in the pond, instead of a circle. So oil can break up into rafts if there is something else on the surface of the water. But from what you said it probably isn't oil causing this.

It seems plausible to me that the microscopic bacteria, perhaps Leptothrix, oxidizing the iron (FeII), are forming these thin layers. One of the links led to a site that talked about the possiblity the bacteria eating the iron becoming slightly magnetized and perhaps orienting to the Earth. So cool!

I would take a sample and look at it under the microscope, or give to a microbiologist at a nearby university to either confirm or rule out a microorganism. I would think this would make a nice project for an upper level undergraduate microbiology major to undertake.

Good pictures. I have many times accompanied regulators on inspections of outdoor scrap storage areas and they see this and ask if we have had an oil spill. The first thing we do is poke a stick in the film and see if it breaks into little "rafts". Iron oxides/hyroxides I suspect, but not sure of the species.

Thanks for the schwertmannite clue Pedro. Now I've found this, which mentions thin films. Beth, I didn't think to use the neodymium magnet I had with me, next time I'll try it.

The puddles are filled by small springs which show ferrous staining. The track the puddles are on, is from an old lead mine, showing considerable siderite on the dump material. The films form at the point of seepage, then go to the puddles where the rafts form. What you see is only an hour or so old, as it had been raining then, which would have disrupted the formations.

Rog, I'm interested in the surface films that you photographed - I also have seen these, and made the (poor) assumption that it was simply due to leaching. Did you, by any chance, touch one of the rafts? I'm wondering if this would produce a thin string of "slime", for want of a better word. I'd love to see these under high power, and will collect some when we are next out. (If you get to do that first, will you please tell us?) So today I have learned something new. Becky

Roger,
What you're seeing is iron bacteria on the water. They derive their energy by oxidising dissolved ferrous iron or sometimes manganese. The result from this oxidisation is ferric oxide, which is insoluble and can produce a rainbow, oil-like sheen on still water. The bacteira also produce an odour similar to rotten lettuce or petroleum which some people describe as "swamp gas".

Curiously, have you noticed this petroleum-like odour around these Roger??



Edited 1 time(s). Last edit at 09/14/2012 07:44PM by Paul Brandes.

Hi Paul,

No, there was no unusual smell. Mind you, the local environment is covered in sheep and grouse sh_t excrement, so it could be difficult to tell! I find the subject interesting - the thin film forms as soon as the water hits air. The film initially has fluid flow, then does the bacteria die or drop off, leaving the schwertmannite film fragile (breaking to form rafts) without its organic binding?

Becky the rafts disintegrate even if you blow on them. Rain or wind destroys them. No slime on the ones I touched. I didn't try the films that were still fluid, having just emerged from the seeps.

I have more photies, if anyone is interested. Kelly, now you mentioned it, I've seen the exact same thing in many scrap-yard puddles. They are totally different to oil films - which also abound in scrappies. Just makes me wonder why I hadn't seen the difference before.

Thanks to all for the input,
Cheers,
Rog

B.C. (Canada) fisheries made me jump thru hoops to prove such sheens were not oil on a property there. A simple test is that a little salt (NaCl) sprinkled on the sheen disperses it. Not sure of the chemistry, perhaps precipitating an iron chloride?

A similar phenomena occurs when sunlight first hits Spruce pyrite. A thin iridescent film forms, reminiscent of bornite. Rainbow colors, easily rubbed off. Any idea what causes this?

Bob

I'll have to try the salt next time I'm up the Dales Bob, that & seeing if a magnet affects the floaters. The formation of pyrite iridescent coating due to sunlight is new, and intriguing to me. Now I think about it, I don't even know what the these light interference coatings on bornite, chalcopyrite etc. actually consist of.... Changing the direction of this thread somewhat, anyone know what compound these beautiful films are?
Regards,
Rog

Hello Roger, I fully agree with Paul B. In an anoxic, wet, sedimentary structure, a consortium of anaerobic bacteria, i.e. sulphate reducers, iron reducers, methanogens to name a few, are doing their thing on available organic matter. Where mineral iron is available in the surrounding clays etc, one of the final mineral products from this bacterial digestion is soluble ferrous iron. Once that seeps to an aerobic soil surface, oxidation quickly occurs and the sheen develops as a monolayer.....very pretty they are too. I have been dealing with landfill management issues for over 20 years and have occassionally been in the somewhat tacky situation of demonstrating to EPA officers that the "oily sheen over there" is not hydrocarbon contamination leaking out but just iron staining. 99% of the time it has been oxidised iron, the other 1% it was hydrocarbon waste,(that time from a defunct coal gas works factory) .A rather cute old oil drillers test to determine if "sheeny" water was in fact oil or not was the camphor crystal spin test. In essence, you carefully scrape some very tiny flakes from a block of camphor with a needle, and allow them to drop onto the suspect sheen. If it is iron staining, the crystals sit motionless. If it is hydrocarbon sheen, the camphor crystals spin eratically around like an ant on a hot plate.

For comparison to your iron seeps, attached are two hydrocarbon seeps, one on a mudflat and the other on the surface of a biological treatment pond. The main visual difference is the hydrocarbon sheens don't seem to break up like mini-icebergs but remain together in sometimes rather stunning patterns.

Best wsihes,
David

Cheers David,
Excellent info & photos to compare! So, some EPA officers seem to be as ignorant of this phenomenon as I was!
Thanks very much, I'll take some camphor with me next time as well,
Regards,
Rog



Edited 1 time(s). Last edit at 09/19/2012 09:52AM by Roger Curry.

Roger,
Actually, local groups of concerned, environmentally minded residents adjacent to a potentially leaking landfill are more of a handfull than a few reasonably scientifically minded EPA officers

David

Amazing thread. I've often seen this phenomenon far from houses and roads, and have just shaken my head at the all-pervasive nature of man's pollution. Remarkable stuff.

These films are common in Florida wetlands. Soil scientists have told me that they are composed of iron and manganese.

This is particularly interesting to me because it is soil science, a discipline of which I know little, but deal with more frequently than mineralogy etc. I suspect that this is one of the redox features, wherein iron (and related metals if present) is leached out of the top layers of the soil and translocated down into the soil column. Unless retained by biological vectors - roots, bacteria, etc.

Great question, answers, and photos!

Very cool and very interesting article.

Roger,
Here is another eye catching effect "sheeny water" can inadvertently produce. This particular water produces identical rainbow patterns as per your first pictures when exposed to the atmosphere. The example shown is a 50mm polypipe elbow that has been delivering groundwater/leachate for about 10 years, the central hole now is a mere 5mm or so. The novel thing with this system is that the water is pumped by an AirWell pump (these are used in potentially flammable/explosive conditions); the pump delivers intermittent slugs of compressed air to drive the water along the pipe to its ultimate destination. Here is where oxygen is added to the system.

Unfortunately, the owners of the site could not see the beauty I saw in this blockage they were just worried abou the cost of replacing 2 km of leachate line

I would be interested if anyone might suggest what this rather pretty mineral deposit might be? The material fizzes slightly in 10% hydrochloric acid and is scratched by a copper nail. The typical chemical composition of the groundwater from which it was formed is as follows (all concentrations are in mg/L).

Sodium 3500
Potassium 150
Calcium 200
Magnesium 670
Iron 0.6
Manganese 0.5
Barium 0.7
Boron 4
Bicarbonate 2200
Sulphate 1200

Obviously a mixture but my first thought of one component might be siderite.............

Very interesting indeed. However I suspect that if you confront irate neighbors or an uninformed EPA official with salt or camphor particles, I suspect that it won't change their opinion in the least except perhaps to make them suspect that you are some sort of snake oil specimen and really not to be trusted. If instead you could site some scientific literature and perhaps a scholarly article on the web, that might stand a chance of changing their minds. Why don't one of the contributors here write an article for Mindat showing examples of both types of iridescent films with some before and after and perhaps during shots of the effect of salt and camphor on these films. That would be something great for Mindat as well as something that might to some extent influence environmental policy. I suspect that an article like that might get picked up on the web and perhaps go a little viral.

Rock Currier
Crystals not pistols.

I agree Rock,
We'll see what happens,
Best Regards,
Rog