How could blue soil exist, in a realistic earth-like world. The world may even be earth.

First off is it even possible - could soil like this exist given the requirements below? (if not then why?)

Mainly what would the composition of the soil be (what elements/chemicals would be present that give the soil its color)?

What shade of blue? (representation could be given in hexcode (#0000FF) or an image maybe)

Would the soil be fertile or toxic or...?

Some requirements:

The soil is just like normal earth soil. All the standard obvious earth soil stuff applies, difference is this soil is blue.

Plants must be able grow in it. Even if just sparsely weeds.

The soil may contain toxins, possibly even be radioactive.

No specific blue, but should be obviously blue, as in not blue-ish-some-other-color, but rather blue. Light blue, dark blue, etc. Blue in the sense that a person who was used to normal soil would clearly describe it as blue.

Solid blue, just as earth soil is solid brown. In other words not brown with little blue rocks or something.

The soil is permanently blue, not temporary.

The soil is not stained or tinted blue, but it's the composition or chemicals/elements in the soil that make it blue. (To me stained or tinted would be something like having the color altered by spilling paint, oil, etc on, etc. or tinted by light or light shining through something like colored glass.)

May be caused by a freak event. (if so what?)

Kind of what I was looking for here (as I thought that blue soil was not actually a thing at all) was actually something that would be more exotic, rare, but realistic, like for example the soil was compromised mostly of two elements that normally aren't found together and it is that combination that causes the blue.




not "blue" (teal, aquamarine)

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    $\begingroup$ Your question is very broad. The constraints you provide are not of the right type to narrow down the answer sufficiently. For example it clearly must be blue, but then you ask is it toxic? Blueness and toxicity are not dependant on one another. You might as well have stated that it must be green and then asked is it toxic? $\endgroup$
    – Slarty
    Oct 8, 2017 at 17:20
  • 2
    $\begingroup$ The soil is not stained or tinted blue, but its the composition or chemicals/elements in the soil that make it blue. That's how stains and tints work... $\endgroup$ Oct 8, 2017 at 21:20
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    $\begingroup$ "Solid blue, just as earth soil is solid brown." Where I am, the soil is quite reddish due to high clay content. But I've also been places where it is almost black. $\endgroup$
    – Asher
    Oct 8, 2017 at 21:33
  • $\begingroup$ ---------------The hex code which you have provided (#00FF00) is 100%green, 0%blue and 0%red.--------------Did you mean #0000ff (which is 100%blue, 0%green and 0%red) ? $\endgroup$ Dec 23, 2018 at 15:10

8 Answers 8


In order to get blue soil

First I would start with a copper rich dirt. Copper is excellent, its a relatively light semi harmless metal that when oxidized turns blue.

Like others have posted: man standing on light blue copper soil

Now to get a deeper blue color

In order to be soil the dirt must contain microbial life and support life. One common byproduct from microbial life is ammonia (NH3). When ammonia is bonded with copper it creates a deep blue indigo compound called ammine (CuNH3):

rich blue vial of liquid ammine

Copper(II) ammine complex Cu(NH3)2+


So what if your copper rich soil contains a prolific microbe that produces a lot of ammine as a byproduct of its existence. The shade of blue can be directly related directly the proliferation of this microbe.

  • $\begingroup$ I want to point out this is a legit hard-science answer $\endgroup$
    – anon
    Oct 11, 2017 at 16:15
  • $\begingroup$ Can you add the source for your blue hills image please? I want to learn more about that place. $\endgroup$
    – Willk
    Oct 24, 2017 at 23:14
  • $\begingroup$ @Will I just did an image search for "blue soil" for the pic. I tried searching for a few minutes to find something meaning for you but couldn't. $\endgroup$
    – anon
    Oct 25, 2017 at 15:47

Soil is not dirt; soil is alive, dirt is inert. Semi-rant about people using non-interchangeable terms over. I would start with the blue-gray mudstone known as Papa which can be a very pronounced blue, (sorry I can't find a good picture of it) the blue colour comes from the iron in the clays from which it is formed, it holds this colour pretty well and forms a reasonable substrate for soil formation. If you keep your soil largely anaerobic, by having high clay content and a high water-table, then you also get blue-ing from cyanobacteria and blue-green algae in the medium, the surface won't necessarily stay blue, especially where weeds are actively growing but it is blue just below the surface and even at the surface where there is no plant growth. If the plants were atmospheric nitrogen fixers, like clover, they'll create higher soil acidity which will reinforce the blue effect.

  • 6
    $\begingroup$ Several years ago I have been in a location near Trento, Italy, with exactly those characteristics. I was a volunteer worker with WWF. I can confirm that the soil was a deep, sick blue (I'd say blue-black, with blue-grey whorls) and stank to high heaven. Weeds and similar plants did grow in it. Farther out, the soil was drier and turned a ruddy brown. $\endgroup$
    – LSerni
    Oct 8, 2017 at 18:36

If I understand what you want correctly, it’s soil that has all the properties of ordinary soil except for its total blue colouration?

For soil to be soil as I think you mean, it must contain at least some organic material so the best candidate would be organic chemicals found in the soil that gave it its blue colour. Many blue coloured organic molecules exist or might be reasonably proposed.

A world in which all light except blue light could be absorbed by plants for use in photosynthesis might work. This would tend to make the plants appear blue as this would be the only wavelength not absorbed. If the material used to absorb all this light (the blue alien equivalent of chlorophyll) were also very stable and not easily decomposed it would tend to build up in the soil and colour that blue as well.


There are quite a few naturally occurring minerals that are blue, inlcuding Lapis lazuli and others. The blue component in Lapis lazuli is lazurite (Fig. 1), which is intense blue. Other blue minerals include azurite, chalcanthite, chrysocolla, linarite, opal, smithsonite, turquoise, and vivianite (see e.g., ThoughtCo).

Lazurite. source: Marin Mineral

Many copper (Cu) salts (or their solutions) are blue, for example copper sulfate (CuSO4) (Fig. 2).

Fig. 2. CuSO4. source: wikipedia)

The Sagada Blue Soil in the Philippines (Fig. 3) is said to be blue duie to its high copper content (but it may be Iron (Fe) too).

Fig. 3. Sagada Blue Soil, Philippines. source: Roamulofied

While the above options are not directly toxic, there are poisonous options too, for example soil contaminated with petrol (Fig. 4).

Fig. 4. Petroleum contaminated soil. source: WA State Dept. Transportation

  • $\begingroup$ Copper sulfate is water solvable; rains would probably wash it away. Fig 3. is more of at teal- not the blue I'm looking for. I'm interested in the first one though. Would it last in through the tests of time? 10000 years of weather, rain, snow, heat, etc. ? $\endgroup$
    – R. Smyth
    Oct 11, 2017 at 14:33

Cainville Utah USA. Southern Utah an area rich in Uranium and is easy to see on Google Maps. The water in rivers and streams in this area will give you gastric distress even when treated or boiled if consumed. The mineral content is unknown to me, but I would expect to find nothing you would want grow anything in. Plants are sparse but exist and are scruffy desert foliage. The whole area is ancient sea bed and mostly sandstone. The area is only 80 to 90 miles or so southwest of Dinosaur land in Vernal Utah. A beautiful landscape as varied as exists on this planet. The blue is clearly visible looking at the Google Earth photos. https://www.google.com/maps/@38.4602117,-110.8388242,5358m/data=!3m1!1e3

  • $\begingroup$ That's more like grey than blue. $\endgroup$
    – Vincent
    Dec 3, 2017 at 23:22

It depends on what kind of soil you mean. Sand is basically just glass, and glass comes in blue. So blue sand is easy, and as some soils are mostly sand, those soils would be blue.

Calcite and dolomite based clay soils are white or really pale. If contaminated with cobalt salts or iron cyanide salts it does turn up blue, sometimes. Prussian blue is insoluble and forms a very fine colloid when left alone, so it tends to linger in the soil. It is 'relatively nontoxic'.

If you wanted to grow a plant in blue soil, I would start with a calcite clay, add cobalt-doped sand and very finely powdered organic material. The organic material is black, which would darken your light blue clay/sand mixture.

At this point it's a trade-off between how toxic you can have your blue dirt be and how blue you want it to be. Generally, you can add as much blue sand as you want, but you'll only be able to grow cacti and palm trees. If you want something more like regular dirt you'll need to add clay and Prussian blue, which will degrade from microbial activity(very slowly, but still). Soil contaminated by Prussian blue as a side effect of coal gasification was once sold as a herbicide, so be stingy with it. As organic matter turns over into the soil it'll darken as more carbon gets incorporated. Make sure to turn the soil regularly, or the clay and sand will settle out into different layers.

All of this does kind of count as 'staining', though. Unfortunately, dirt is made of silica and organic matter, and neither of those can be blue without additives or something really exotic going on. Blue is often a 'structural color' in nature, but that kind of color requires a reasonably ordered crystal to work, which is not really how dirt works.

  • 2
    $\begingroup$ Sand is not glass. Sand is crystalline, glass is vitreous. $\endgroup$
    – AlexP
    Oct 8, 2017 at 17:35
  • $\begingroup$ Sand and soil are kinda two different things. Given the case you described it would be fine blue glass not sand, which is way different. Prussian blue is interesting though, the question is, would it be permanent, in other words 10000 years later after rain, sun, snow, etc. would it still be blue? $\endgroup$
    – R. Smyth
    Oct 11, 2017 at 14:29
  • $\begingroup$ @AlexP Dumortierite is a blue quartz-like crystal incorporating boron instead of cobalt. Same principle, but different metal ions. As far as Prussian blue is concerned the remediation recommendations are to turn it over regularly to 'expose it to air and microbial activity'. I doubt it has that thousands-of-years permanence you're looking for. $\endgroup$
    – Resonating
    Oct 12, 2017 at 15:59

Thinking outside the box, here. It's entirely possible. The soil could even be normal, Terran soil. The light shining on it could be blue, though. As O-type stars are really rare, and not recommended for life, let's go with a B-type, a blue-white, or light blue star. If you place a planet in orbit of one, you're going to have blue soil.

For your color requirement, here's a nice picture of Bellatrix, a example of a B-type star that's 250±10 light years off.

Now, would the soil be fertile? The main issue is of how long these stars live. It's not very long. Enough for planets to form, but the star will go nova or supernova before then. You could always terraform one of those molten rocks, or build a megastructure like a shellworld there.

  • $\begingroup$ Cool idea but this would be what I would consider as tinted. $\endgroup$
    – R. Smyth
    Oct 11, 2017 at 14:24

Well, here are a few possible elements that could be in your soil:

  1. Copper. While copper in the form of pots, pans, and bronze is a reflective brown, copper in the soil is actually a pretty blue. This is because, while the copper in the aforementioned pots is from the anaerobic depths of the earth, the copper in soil is oxidized. Since it is water soluble it would not make your soil uniformally blue, but this is the closest you can get without poisoning the soil.
  2. Cyanide salts. Not only do these make soil a very pretty blue color, their presence makes the air smell like peaches.* Of course, they would also kill all the local fauna, but that is just a "minor" problem.

  3. Cobalt. This would make your soil a very uniform (if somewhat boring) blue, but it would also kill all the local flora.

Of these choices, I prefer copper. While it will not yield the uniform blue you desire, it is the only safe option if you want the area to be inhabitable.

*Actually, to be technically correct, cyanide does not smell like peaches; it is the peaches that smell like cyanide. This is because peaches contain large quantities of cyanide in their flesh and pits.


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