We find in the book Minerals and their Localities by Jan H Bernard and Jaroslav Hyrsl several chemical formulas containing a square. What does this square means? An example: Franciscanite $\ce{Mn3 (V,\square)(O,OH)3 (SiO4)}$

Thanks for your answer for I have been looking for answer for a long time.


1 Answer 1


That square refers to a vacancy (or framework vacancy) in the crystal structure. Here's one reference from Advances in Electronic Ceramics. Ceramic Engineering and Science Proceedings. Volume 28, Issue 8. Ed. C. Randall ${\it et\;al.}$

In short, a framework vacancy is a feature of some inorganic materials in which a "guest atom" (or more than one) can fit into the structure or denotes a structure that is missing interstitial or packing atoms (as outlined here).

Here's the info on your mineral where you can see that the square is instead denoted by square brackets [].

  • 2
    $\begingroup$ Note that, according to IUPAC recommendations, a square box ($\square$) is indeed used for vacancies in certain contexts, but the use of italicized $V$ is preferred, the element vanadium being written with the upright letter $\ce{V}$. $\endgroup$
    – user7951
    Aug 30, 2015 at 10:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.