I have a problem with the "Star Trek Canon" on Vulcan Blood. Here is the situation:

Vulcan blood is green colored due to using Copper instead on Iron

The color of blood differs according to the presence or absence of respiratory pigments and the type of pigment used by an organism. Hemoglobin transports oxygen (or carbon dioxide) using iron, thus humans have blood that is colored red. Many deep sea arthropods and some molluscs use hemocyanin which gives their blood a faint bluish color due to the presence of copper. Thus hemocyanin (which Star Trek Script Geniuses deemed the proper protein molecule of the vulcan blood) was actually supposed to be the Andorian blood, because they have BLUE colored blood and they live on a FROZEN world (which matches the Earth deep sea environment of the arthropods and molluscs).

What would actually be (in-universe terms) the metal running in the protein molecule which could taint a Vulcan's blood green? (right now I'm interested in the metal taint only; the reason for it I may be able to come up with (role-play game))

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    The way this is phrased, it sounds like it’s asking for a real-world analysis of green blood, which would be off-topic. You could rephrase it to say that you’re asking for an in-universe explanation of their blood color.
    – Molag Bal
    Apr 1, 2016 at 16:39
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    See this answer on Worldbuilding for some possible blood colors and the metals they use. Looks like copper blood should be blue, but chlorocruorin can be green. Apr 1, 2016 at 16:52
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    I don't know, but I'm not sure that there's going to be much in-universe explanation, other than, "it's copper." "But that doesn't make sense!" "I said, it's copper!"
    – Molag Bal
    Apr 1, 2016 at 16:52
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    @DJClayworth I did the google search "site:chakoteya.net vulcan copper" along with "site:chakoteya.net spock copper" (chakoteya.net has transcripts of every Trek episode) and a reference in "Obsession" where Spock said "My haemoglobin is based on copper, not iron" and another in the animated episode "The Pirates of Orion". I guess if one wants an in-universe explanation for why it's green rather than blue, one could imagine the molecule contains both copper and some other metal like Vanadium, which can create green blood on its own.
    – Hypnosifl
    Apr 1, 2016 at 16:55
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    ...for example, there is apparently a copper vanadium oxide molecule, so perhaps it would be possible to have a metalloprotein analogous to hemoglobin which binds to oxygen and contains both copper and vanadium, with the vanadium giving it a more greenish color. You'd have to ask a chemistry expert whether there'd be any flaws in the idea though.
    – Hypnosifl
    Apr 1, 2016 at 17:24

1 Answer 1


It was established in the TOS episode "Obsession" that Spock's blood uses copper: from the transcript here, he said "My haemoglobin is based on copper, not iron." As you note, in real organisms that use copper-based metalloproteins to transport oxygen in their blood, the blood is bluish when oxygenated (and it's clear when de-oxygenated). This article notes there are some organisms with metalloproteins that use the element Vanadium, and they do have green blood:

Another naturally-occurring blood pigment, vanadium chromagen, is found in sea squirts, ascidians, and tunicates. Contained within tiny corpuscles known as vanadocytes, it usually makes blood apple-green, though this may change to blue or orange in the presence of different vanadium oxides.

According to this wiki article it's actually not certain that vanadium chromagens (also known as Vanabins) actually serve the role of oxygen transport, although this is one hypothesis.

Anyway, if vanadium-based metalloproteins can be used for oxygen transport, perhaps we could imagine a metalloprotein that uses both vanadium and copper; there are molecules containing both along with oxygen, like copper vanadium oxide, though this isn't itself a protein and I doubt any organisms on Earth have proteins like this. You'd have to ask an organic chemist whether a protein containing both copper and vanadium would actually work for oxygen transport, and also whether there could be proteins like this that would give a green color like the vanadium chromagens (the quote above notes different vanadium oxides can change the color), but this at least seems like a semi-plausible way of reconciling the green color with Spock's statement that his blood uses copper.

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    It sure does, Copper Vanadium Oxide for Vulcans and pure Copper for Andorians it is. :) Apr 2, 2016 at 17:03

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