I am using the \usepackage[version=3]{mhchem} package, and would like to write the formula for Dolomite in my report: (Ca,Mg)CO3

So far I haven't found a way to get that comma right in my formula using the mhchem package, and haven't found anyone having had troubles doing that so far. Anyone could help me doing so?


  • 2
    Dolomite is CaMg(CO3)2. What you write, (Ca,Mg)CO3 is Mg-rich calcite that is a different mineral to dolomite and has different crystal structure and properties.
    – Gimelist
    Aug 18, 2019 at 5:22

1 Answer 1


The OP's formula (Ca,Mg)CO3 is completely fine and meets IUPAC recommendations [1, p. 21], section IR-

(d) In solid-state chemistry, to enclose symbols of atoms occupying the same type of site in a random fashion. The symbols themselves are separated by a comma, with no space.


  1. K(Br,Cl)

To achieve this with mhchem, the sane way would be to use braces around the comma (as mentioned in the comments): {,}. Note that chemformula doesn't require the comma to be escaped and renders the formula correctly "as is":


        modules = all


\ce{(Ca{,}Mg)CO3} (\texttt{mhchem})

\ch{(Ca,Mg)CO3} (\texttt{chemformula})



  1. IUPAC “Red Book” Nomenclature of Inorganic Chemistry, 1st ed.; Connelly, N. G., Damhus, T., Hartshorn, R. M., Hutton, A. T., Eds.; IUPAC Recommendations; Royal Society of Chemistry: Cambridge, UK, 2005. ISBN 978-0-85404-438-2. PDF

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