Is this creek… rusting?

A few times when on hikes I’ve come across a weird orange patch in a creek. This is different than just a section of water that’s turned orange from red clay run-off – this is a distinctive orange section of an otherwise clear stream:

Photo by Heather Wall

Notice that the water on the left is clear and running smoothly over the rocks while the slower-moving water on the right is orange. Is it pollution? Is it dangerous? Should I not let my dog near it? These pictures are from the creek that runs through our yard, so that question became even more urgent. Based on the distinctive coloring, I even began to wonder…

Is this creek… rusting?

So, of course I did some research and the short answer is… yes! Groundwater has carried bits of iron deposits to the surface where an underwater spring has bubbled up. At that point an iron-oxidizing bacteria formed that feeds off the iron deposits – the bacteria are basically eating the iron to produce energy in the same way that other bacteria eat organic material to survive.

If you look closely at the photo, you can see the gel-like formations that are the bacteria. Fortunately, the bacteria are not harmful to people or animals. It’s a purely natural phenomenon. Sometimes it can result in a bad odor or the water tasting funny, and if it gets into a drilled well the clumpy bacteria can clog up the system, but it won’t hurt you (or your dog).

Sometimes this same bacteria also causes an oily sheen to the water as it oxidizes the iron:

Photo by Heather Wall

In the past when I’ve seen this, I’ve worried that pollution has gotten into a creek somehow, but it’s just the results of a natural oxidizing process. To make sure, you can poke it with a stick – if it breaks apart easily, it’s the natural bacterium. However, if it clumps up and attaches to the stick, it’s probably a petroleum product and means the creek has become contaminated.

Knowing that we had rusty spots in our creek was a relief (it’s not dangerous!) and interesting (we have iron-enriched water!) but it also raised another question connected to gold mining…

A few months ago, we played around with gold mining in our creek. It makes sense – we’re only a few miles as the crow flies from the “Gold Rush area of the South” in Dahlonega, Georgia. After my husband spent hours and days panning for gold in the creek, we found that we do not have gold in them thar hills, but we do have plenty of black sand, which is often found hand-in-hand with gold deposits.

Black sand is heavy and dense, and can often be found with gold at the bottom of crevices and pools. It turns out, it’s also magnetic:

Photo by Heather Wall

This sand is from a handful we sifted multiple times, in order to get out the “regular” blond sand. You can see from the photo that we still have some regular sand bits mixed in.

If this black sand is magnetic, it must also be a source of iron just like those rusty spots in the creek, right? And if that’s the case:

Why isn’t the black sand rusting?

It turns out that black sand is actually made up mostly of magnetite, a mineral ore that’s the most magnetic of all natural minerals on Earth. When miners find large deposits (not just sandy bits), they can smelt it in furnaces to make steel.

Why doesn’t it rust? It turns out that magnetite already IS rust – just not the red kind. It’s already oxidized, meaning it has come in contact with oxygen.

It’s also interesting to know that our bodies can produce magnetite – it’s mostly found in our brains. It’s one reason MRI machines work on our bodies: they create Magnetic Resonance Images. Some researchers suggest that the magnetite in our brains should help us sense the Earth’s magnetic field and create a sort of mental compass – a sixth sense. Magnetite has been found in bird beaks and fish noses and is thought to help them orient themselves while migrating. Some people, including the Inuit and Aboriginal Australians, seem to have an enhanced sense of direction, and the thought is this could be due to magnetite in their brains.

This was a long rabbit trail to go down just based on an orange patch in a creek, but it just goes to show how amazing nature is and just how much there is to learn about it.

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Detritus:

• Did you know? Georgia clay is red because of iron oxides

• More about magnetite as the body’s hidden compass

• This guy shows how to collect iron ore from black sand and explains how it was used by ancient peoples

• What is the world’s largest magnet?

Have you come across one of these orange patches in a creek? Or found magnetized sand? I’d love to hear your thoughts!