"Resistivity" is the inverse of the conductivity when this inverse exists.
Applicable units are those of quantitykind:Resistivity
http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=31891
http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=121-12-04
https://cdd.iec.ch/cdd/iec61987/iec61987.nsf/ListsOfUnitsAllVersions/0112-2---62720%23UAD161
"Resistivity" is the inverse of the conductivity when this inverse exists.
$\rho = \frac{1}{\sigma}$, if it exists, where $\sigma$ is conductivity.