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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!

Asphaltenes.

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 the tar. If your creatures had circulating tar-like substances in their blood, 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.

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.