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I'm writing a space game that I want to give a more "realistic" feel. When looking for a reference as to distribute elements in planets (for mining, etc) Instead of finding the more usual percentage tables, it seems that all elements are presented in a "normalized to Si 10 to the power 6", and furthermore, it seems that the data is presented as number of atoms, instead of actual mass. I've been searching this for days, and even the "parts per million/billion/trillion" tables sometimes just jump for percentages, where is is again no clear if what is being referred to are masses or number of atoms. Could someone clarify this, or better, point me to a mass percentage table of elements in a solar system/galaxy for reference? Thanks in advance.

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Could you please provide a link to that table? Maybe it is easier to interpret it directly than from your explanation. –  Envite May 21 at 8:44
    

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The table you referenced is normalized so that the abundance of Silicon (Si) is exactly $10^6$, and all the other numbers are related to that.

"Abundance" in this table refers to the number of atoms.

Please note that this table is for the entire Solar System, taking into account the huge amounts of Hydrogen and Helium in the Sun. It will not be appropriate for creating Earth-like planets.

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Sure :) I'm differentiating planets in my software depending on other data, but I wanted to have some reference when distributing, say, how much Yttrium we might find on a mainly silicates planet. So to find the relative mass, I'd have to convert the number of atoms to masses, right? My chemistry is a bit shaky, but I have a "moles and Avogadro" feeling about this, and that it will be a lot of work :) Many thanks for clarifying this. –  Jorge Al Najjar May 21 at 9:11

It simply means that the scale is such that the relative abundance of silicon is $10^6$. For example, if you see a statement on this scale that in atom number $\mathrm{C} = 1.17\times 10^7$, that would tell you that carbon atoms are $11.7$ times as numerous as silicon ones.

What you're probably looking at is sometimes cosmochemical scale, normalized to this way. A common alternative scale in astronomy is to measure things in $10^{12}$ hydrogen atoms and logarithmically (so that abundance of hydrogen is exactly $12$ and $11$ would mean one-tenth as abundant as hydrogen).

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