/ʃ/ or /s/ with the termination -ciate? Both realizations occur, but when?

I have noticed that among the several words that have the termination -ciate (or derivatives of these) sometimes the pronunciation of the 'c' is /ʃ/ and sometimes /s/. That is, sometimes palatalization occurs (as in "attention" or "commission") but some other times it doesn't. For example:

/ʃ/: Emaciated, excruciating, officiate.

/s/: Pronunciation, enunciate, glaciated.

(according to the dictionaries I checked)

Is this arbitrary? Is there any pattern/rationale behind when it is one or the other? Or in other words, can one predict if palatalization occurs by looking at the part of the word preceding -ciate?

Solution 1:

Thanks to @PeterShor and @Decapitated Soul for the insightful comments.

It seems /ʃ/ is mostly pronounced after a vowel, and also /ʃ/ tends to be pronounced when the vowels in "ciat" are not stressed. So my conclusion is:

• It seems there is some variation between speakers and between dictionaries, but using /ʃ/ after a vowel and /s/ after consonant seems to work (in the sense that there are people that pronounce it that way).

• Using /ʃ/ if none of the vowels in "ciat" are stressed seems to work mostly but there is at least two counterexamples: enunciate and appreciation (the latter is probably like that because it inherits the pronunciation of appreciate). However, this second rule seems to extend better to other kinds of palatalization under different patterns. Like in "palatalization" or "attention" :)

A longer list of examples:

/ʃ/: associate, appreciate, appreciation, depreciate, disassociate, emaciated, excruciating, glaciated (this is part of the mentioned variation, some dictionaries say it's /ʃ/), glaciation, officiate, unappreciated.

/s/: denunciation, enunciate, pronunciation, renunciation.