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Floating Hematite?

Posted by Roger Curry  
Roger Curry September 14, 2012 12:47PM
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?


open | download - FePuddle1.jpg (464.2 KB)
open | download - FePuddle2.jpg (377.9 KB)
open | download - FePuddle3.jpg (340.4 KB)
Roger Curry September 14, 2012 12:49PM

open | download - FePuddle4.jpg (277.6 KB)
open | download - FePuddle5.jpg (487.9 KB)
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Pedro Alves September 14, 2012 03:19PM
Hello Roger,
my guess is Schwertmannite.

Pedro Alves
Beth Schaefer September 14, 2012 03:48PM
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.
Kelly Nash September 14, 2012 04:21PM
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.
Roger Curry September 14, 2012 05:25PM
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.

open | download - FePuddle7.jpg (525.7 KB)
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Becky Coulson September 14, 2012 08:19PM
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
Paul Brandes September 14, 2012 08:43PM
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 08:44PM by Paul Brandes.
Roger Curry September 14, 2012 09:54PM
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,
Bob Jackson September 19, 2012 12:11AM
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?

Roger Curry September 19, 2012 07:09AM
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?
David Sheumack September 19, 2012 08:33AM
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) :-D .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,
open | download - river seep.jpg (368.6 KB)
open | download - Summer DNAPL eruption.jpg (35.3 KB)
Roger Curry September 19, 2012 10:49AM
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,

Edited 1 time(s). Last edit at 09/19/2012 10:52AM by Roger Curry.
David Sheumack September 19, 2012 11:35AM
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 :-D

David ;-)
Tim Jokela Jr September 19, 2012 04:36PM
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.
Anonymous User September 19, 2012 09:10PM
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!
Byron Thomas September 19, 2012 11:22PM
Very cool and very interesting article.
David Sheumack September 20, 2012 05:24AM
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 :-D 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.............
open | download - Leachate line blockage.jpg (117.4 KB)
Rock Currier September 20, 2012 08:02PM
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.
Roger Curry September 20, 2012 10:12PM
I agree Rock,
We'll see what happens,
Best Regards,
Paul Brandes September 20, 2012 11:49PM
In my "real" job, I work closely with the USEPA and I will say they are a unique bunch when it comes to the environment; they definitely have a different take on enforcing environmental regulations than we do. And I do agree David in that a group of environmentally minded citizens with very little knowledge of anything can be more of a challenge. They all make my job very interesting somedays.......

As far as an article Rock, that sounds like a grand idea!
David Sheumack September 21, 2012 08:57AM
Rock, I should clarify that the mentioned camphor test is not a novel regulatory test but a mere kiddy demonstration, that works sometimes and can show the change in surface tension properties of water and hydrocarbon contaminated water. In my work, regulatory protocol specifies that when a seep is detected and assessed, the usual protocol is: exclusion zone around the area, jump into your PPE dress, PID assessment of immediate air space, fill numerous bottles with observed seep liquid and transfer said bottles asap to the lucky laboratory that has been asked for a 24 TAT for VOCs, TPH, PAHs, heavy metals to name but a few, then convey the results to regulators (first) then community (second). That process satisfies the regulators, but there will always be a few doubting citizen Thomas' and Marys' that have to be handled carefully, that's the part of the job that I find fun. ;-)

On the subject of amusing snake oil salesmen, I mentioned that I originally heard of this camphor test from an old rigger. Many years ago when my wife and I moved to our property, we decided to put a water bore down, we are not on a municipal supply. It was a rather expensive job and we got two quotes. The first "old timer" advertised "free divining and no water, no pay". He turned up and wandered around the property for an hour or so with a bent bit of wire which occassionally twisted around, and he never stopped talking. Finally he said "this is the spot and I can also tell you if we hit coal or oil shale during the drilling!!" He then produced two bottles of water one pure and the other with "a touch of hydrocarbons" and then performed the mentioned little test. The second driller turned up, knowing that Mr X had also been quoting. First question he asked was "where did X say was the best place to drill for water?" I showed him, he laughed, and said "looks like the easiest spot to set a drill rig up on this bloody hillside". Next comment he made was "you know, if you drill down 100m, you are guaranteed groundwater ANYWHERE along the eastern coast of Australia."
The boss said the first fella talked too much so we hired the second bloke, and yes, hit water at 76m, it produces a decent volume :-) but alas also a stunning iron stain when exposed to air :-( Subsequent analysis showed a TDS of 3000 ppm and Fe of 2 mg/L and Mn of 0.6 mg/L.
Roger Curry September 21, 2012 04:36PM
Iron-depositing bacteria and their geologic relations by Edmund Cecil Harder, 1919
Online here
Iridescent films mentioned on pages 18 & 48
David Sheumack September 22, 2012 06:39AM
Hi Roger,
Yes, there is quite a bit of info on "floating films" out in cyber land. This one certainly gives a good summary of man made and natural.

Roger Curry September 30, 2012 02:37PM
Hi all,
Just got back from Teesdale, a neodymium magnet has no effect on the floating films. I also collected some of the wildly coloured film together, to see what its actual bulk colour is. Unsurprisingly, rusty. Also noticed that, on agitation, the mineral film breaks into tiny particles which sink giving a beautiful spangly effect when the sun (briefly) shone. The mineral is therefore not hydrophobic like an oil film, and is supported by surface tension, having formed there.
Claire Milloy August 26, 2013 04:44PM
After reading the above posts, I found the following information:

United States Geological Survey - What's the Oil On the Surface? http://pubs.usgs.gov/gip/microbes/index.html#anchor4816506

Central Utah Water Conservancy District: http://www.cuwcd.com/operations/waterquality.htm

Arlington Virginia, Stream Pollution.... http://www.arlingtonva.us/departments/EnvironmentalServices/wpcp/StormSewer/EpoReportingStreamPollution.aspx
Roger Curry August 27, 2013 12:08AM
Nice links Claire!
Excellent info,
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