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In my game there are crystals/gems/rocks which change hue shifting continuously the full spectrum of red-blue-green colors, the change in color is random and some times it slows down and stays the same color for a while longer than usual before shifting again.

random: implies that the change in color is mathematically hard to predit and not influenced by how lights are shined throu at specific angles, in real life some objects have different colors based on how they are angled towards light. this is not the case here. Two crystals in the same position, same angle and of the same shap or weight and volume may still display different colors.

The mechanism that makes the crystals shift in colors can also work in biology, some animals use those crystals to have parts of their bodies that shift and change colors.

The crystals can also be smashed into powders to make paints, when in powder form the crystal stops changing colors but when mixed with a secondary "handwavium" all powder particles shift color together as if they were one crystals.

This way the paint can be used to dye skin, hair, teeth, cloth, wood and various other things.

handwavium: I lack the knowledge to explain another mechanism so this is just a placeholder.

So how could I explain the color shifting properties of this crystal?

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    $\begingroup$ handwavium is the nest you are going to get, a crystaline solid constantly changing chemical properties in many diffrent configurations is essentially impossible. All the crystals shifting together is the least of your problems. $\endgroup$
    – John
    Dec 30, 2023 at 15:46
  • $\begingroup$ If this is for a game you really don't need an explanation at all $\endgroup$
    – M S
    Dec 30, 2023 at 22:57
  • $\begingroup$ @MS lore n stuff $\endgroup$
    – Xenophile
    Dec 31, 2023 at 0:32
  • $\begingroup$ Which period or rather what setting? If futuristic then try QD-OLED or holographic projection, else magic crystals🤔 $\endgroup$
    – user6760
    Dec 31, 2023 at 5:37

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Sadly, this is impossible under real physics.

You might be able to make crystals that started as one colour and gradually changed to a different colour as they cooled, underwent radioactive decay or otherwise moved to a state of lower energy an/or higher entropy. But once they have reached that state, they'll stay there unless something is done to them.

Thermodynamics is simple, and cruel to many schemes.

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Maybe time crystal is what you are looking for:

In condensed matter physics, a time crystal is a quantum system of particles whose lowest-energy state is one in which the particles are in repetitive motion. The system cannot lose energy to the environment and come to rest because it is already in its quantum ground state. Because of this, the motion of the particles does not really represent kinetic energy like other motion; it has "motion without energy".

In theory, it's could be possible that you can make a time crystal whose oscillations affect the color, and where there oscillations are so complex that they cannot be predicted.

However, you cannot pulverize time crystals to make paints: they would no longer be crystals (but this pertains to all crystals). You need to retain at least some of the crystal structure. Also, the unpredictability will probably suffer when the shards get smaller and smaller because the interactions will become less complex.

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  • $\begingroup$ I do not see how a macroscopic piece of any kind of material could possibly be in its lowest energy state at any non-zero temperature. (And if the material is illuminated by a light source so that it can show color then it will of course no longer be in its lowest energy state.) $\endgroup$
    – AlexP
    Dec 31, 2023 at 1:41
  • $\begingroup$ @AlexP In material science, they apparently don't bother explicating that it's not the globally lowest energy state, they just say lowest-energy state when they are talking about local minimum. Lowest-energy state is used also when they talk about memory metals. Eg. "[...] both B19 and B19′ are energetically more stable than the parent B2 phase, and B19′ is the lowest-energy state with the correctly predicted distortion angle." sciencedirect.com/science/article/abs/pii/S1359645408008665 $\endgroup$ Dec 31, 2023 at 2:02
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As John states in another answer it is probably not possible to obtain exactly what you're looking for without resorting to handwaving it or sticking a bunch of coloured LEDs inside a colourless crystal.

There are a few ways crystals can change colour. The most common are through phase changes and through the introduction of new impurities/dopants. In the case of impurities and dopants these aren't useful for you because it requires the crystal to be exposed to a source of the dopants to produce a colour change and so isn't going to give the kind of continuous changes in colour you're looking for.

Phase changes are a little more useful to you. These are when the structure of a mineral changes configuration. While most phase changes need high temperatures and/or pressures to occur liquid crystals can change colour over a pretty narrow temperature range and are probably the closest to what you are looking for. These crystals have a series of semi-ordered phases which have properties between an ordered crystal and a disordered liquid. In these semi-ordered phases the molecules form layers. As light passes through the layers it is reflected and interferes with itself. Some wavelengths interfere constructively ad become stronger while others interfere destructively and become weaker. The stronger wavelengths determine the colour of the mineral. Changing the temperature changes the spacing of the layers and so different wavelengths will dominate. These crystals can give any colour of the spectrum depending on temperature. Unfortunately these colour changes are based on temperature and so are distinctly not random. The crystals are also liquids but this can easily be solved by having them encased in some kind of shell (which is pretty much what the "stone" in a mood ring is). If the shell is itself tinted or has odd optical properties this could further modify the colour observed and give a larger range of possible colours.

We now have a crystal that changes colour through the whole spectrum but it isn't random. To get our randomness we need to introduce another material into our crystal. Radioactive material generates heat. If very small pieces of a radioactive material were suspended in the liquid crystal above then this would create hot areas around the radioactive material and cool areas far away from them. These different areas would have different layer separation and so would reflect different wavelengths. As light passes through the liquid the end colour would depend on what hot and cold spots it passed through. If the radioactive material moves randomly through the liquid this would mean the light passes through different patterns of hot and cold spots and so would give randomly shifting colours.

Conveniently this also explains the powder and biology parts. Grinding up into powder distributes the radioactive isotope evenly and so loses the temperature fluctuations. If you want you can also claim that breaking the shell and exposing the liquid to air causes it to solidify (probably due to oxidation) and so it will lose it's colour changing properties entirely. The biological part can be explained by animals controlling blood flow to the crystals and so altering the temperature that way.

A note of caution I am not convinced the science here stacks up. This is a long way from my area of expertise and its hard to find sources for a material I have entirely made up.

It's also worth saying that the complexity of the above material (a combination of three kinds of material in a specific configuration, two of which have very specific properties) is very unlikely to occur naturally. I suspect people will find it more believable if you just handwave the crystals than if you try and use my explanation and claim they formed naturally.

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The crystal itself is transparent and quite mundane to look at. The color-changing effect is caused by a living organism that adheres to the crystal. This organism is a bit like a coral, it lives its whole life on the crystal and feeds on particles passing through the air.

The organism consists of microscopic layers of translucent material joined by organelles that allow it to expand and contract, forcing air between the layers and giving it more to feed on. As mentioned in Bellerophon's answer, the overall color of the organism depends on the distance between these membranes and the interference they create in the light passing through. If the organelles happen to expand more than average, or contract more than average, they can shift the overall color.

In their normal crystal habitat, the organisms' membranes knit together into large sheets following the plane of the crystal. The relatively stiff membrane keeps the spacing of the layers fairly similar across the width of the sheet, although the spacing and therefore color will slowly drift with the vagaries of the different organisms' movements.

If the crystal is shattered, the link is lost and each part of the sheet will flex independently. If it's ground up or washed off, the organisms die altogether and the color-shifting stops.

However, if you know the special technique, and apply just the right kind of solvent, you can lift the entire sheet right off the crystal while it's still alive, and apply it to the surface of your choosing. It will continue to live there (for awhile, at least) and change colors as it did on the crystal.

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