Friedel's salt is a layered double hydroxide (LDH) of general formula:
or more explicitly for a positively-charged LDH mineral: 
or by directly incorporating water molecules into the Ca,Al hydroxide layer:
where chloride and hydroxide anions occupy the interlayer to compensate the excess of positive charges. 
In the cement chemist notation (CCN), considering that
and doubling all the stoichiometry, it could also be written in CCN as follows:
A simplified chemical composition with only Cl in the interlayer, and without OH, as:
can be also written in cement chemist notation as:
Friedels salt is formed in cements initially rich in tri-calcium aluminate (CA). Free-chloride ions directly bind with the AFm hydrates (CAH and its derivatives) to form Friedels salt.