mons petrae / mons petrosus [noun in the genitive used adjectivally?]

Hi, there.

I hope that this question does not appear highly sophomoric, as I am sure some of my questions do.

Today, I am questioning whether a noun in the genitive case can be used adjectivally within a sentence in Latin. For instance, are the following constructions valid as replacements for the given correspondents: Ecce mons petrae for Ecce mons petrosus, Ecce mons lapidis for Ecce mons lapidosus, Ecce mons saxosus for Ecce mons saxi for...

mons petrae / mons petrosus [noun in the genitive used adjectivally?]