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I am currently working in a "fantasy" world without any kind of magic and I thought of a race with different skeleton color (blackish in particular but I want to know in general). I am not well versed in biology but may I guess the white in our bones is from the calcium phosphate that forms them?

So, is there any other component that could realisticly (to a certain extent) form an skeleton of different color? In particular black/grey. Maybe there is a way of getting pigmented bones by adding other component to the mix?

Hope I made myself clear as I could not find any information related to this topic in these forums nor other. I would love to keep my world as realistic as possible.

Thanks in advance for your answers!

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    $\begingroup$ There is a breed of chicken that has black bones (Silkie) $\endgroup$ – Henricus V. Aug 25 '19 at 5:39
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    $\begingroup$ Wow never heard of them but it's very interesting how melanin not only affects their skin but also their bones and organs, though I could not find any information about why this occurd guess was a DNA variation that's all. $\endgroup$ – DigiAB Aug 25 '19 at 11:20
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    $\begingroup$ Unless some creatures have bones on the outside nobody will see the color of their bones until they are badly injured or dead. I note that human bones are usually brownish and exposed bones are eventually bleached white by sunlight. $\endgroup$ – M. A. Golding Aug 25 '19 at 16:12
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Like bones, which are made of calcium phosphate, seashells are made from a calcium compound, calcium carbonate. Calcium cabonate is white, like bone, and yet many mussels build colorful shells. In fact, some mussels are black:

black mussels

The colors in sheashells comes from pigments. So the bones in your story contain black pigment.

The evolutionary purpose of the black chemial might be that it:

  • prevents a certain infection of the bones because it is antifungal, antiviral, antimicrobial, antiparasitic or the like
  • makes the bones more stable / flexible / harder
  • serves no purpose but is contained in the food and is chemically prone to bind with some component of the bone
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Bones are whitish because of their chemical composition. When alive, bones are white~yellow~red because of the mineral, fat and bloody components. Dead dry bone is white because of calcium phosphate which makes up a large portion of the mineral content.

In order to get another colour, you have two choices:

  1. Start all over by reinventing biology. Choose a different evolutionary path that will use a compound other a metal phosphate mineral.
  2. Look for similar metal phosphates that have other colour schemes.

You could try something like herderite, which is calcium beryllium phosphate. It can be greenish or yellowish or clearish. I make no guarantees about the primary world biological validity of such a substitution, because a) handwavium and b) fantasy world necessities and all. You'll have to do some homework on your own, but I think this will give you a possible line of research! I'll only note that most metal phosphates seem to be whitish or have muted colours. You may need another additive to get black bones.

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  • $\begingroup$ I've been doing some research and I found out about the Lithium iron phosphate (LiFePO4), naturally present in Triphylite, is black/grey when powdered. Maybe part of the calcium phosphate in their bones has been replace by this component? I don't have enough knowledge in biology to analize as you said the validity of this component in someones body, but our body is already full with iron in the blood so, I supose is compatible. Also Lithium is a bit toxic so the presence in a body might do some harm but I guess they could have developed inmunity to it. I'll keep searching, thank you so much! $\endgroup$ – DigiAB Aug 25 '19 at 11:41
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Asphaltenes.

smilodon tar stained skeleton

https://commons.wikimedia.org/wiki/File:Smilodon_californicus_saber-toothed_tiger_(La_Brea_Asphalt,_Upper_Pleistocene;_Rancho_La_Brea_tar_pits,_Los_Angeles,_southern_California,_USA)1(15420357246).jpg

The bones retrieved from the La Brea tar pits are stained an impressive greasy black. That is from sitting in the tar after they died. If your creatures had circulating tar-like substances in their blood from their food supply, their bones might be stained black in life.
Asphaltenes is the catchall for these persistent gooey hydrocarbons as they occur in tar pits and elsewhere.

Asphaltenes consist primarily of carbon, hydrogen, nitrogen, oxygen, and sulfur, as well as trace amounts of vanadium and nickel... Asphaltenes are defined operationally as the n-heptane insoluble, toluene soluble component of a carbonaceous material such as crude oil, bitumen, or coal. Asphaltenes have been shown to have a distribution of molecular masses in the range of 400 u to 1500 u, but the average and maximum values are difficult to determine due to aggregation of the molecules in solution. The molecular structure of asphaltenes is difficult to determine because the molecules tend to stick together in solution. These materials are extremely complex mixtures containing hundreds or even thousands of individual chemical species.

I could imagine circulating globs of asphaltene might contribute to accelerated blood clotting, or serve an immunogenic role in sticking to and inactivating parasites. Imagine a mosquito drying to drink blood containing this tenacious goo.

In addition to black bones, your creatures would smell like tar and have thick black blood. If you heated it enough, once you boiled off the water the residual asphaltenes would burn and probably produce a lot of dirty brown smoke.

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  • $\begingroup$ Just to be clear: you’re saying the bones at La Brea are black because the nearby creature’s got lots of tar in their diet? Or is it because they’ve been sitting in tar? $\endgroup$ – SRM Aug 24 '19 at 22:00
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    $\begingroup$ @SRM The bones from La Brea are black because they have been sitting in tar for ages. $\endgroup$ – user67090 Aug 25 '19 at 12:16
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    $\begingroup$ I made a small edit to clarify that point. $\endgroup$ – SRM Aug 25 '19 at 18:21

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