Chœur, chorale, chiasme, echo, dichotomy are all pronounced [k]. For a consonant after the ch, we have: strychnine, chlore, chronomètre, chthonien, chrysanthème, Chaldée, scholastique, chiromancie, orchestre, orchidée, schizophrénie, psychologue, chrétien, chélidoine, chorégraphie ... looks to me like the Greek origin of all those words led to a [k] sound. Those ch were χ in Greek, and that would be the rule, rather than a rule depending on what's before or after the [ch]. A rule with exceptions no doubt.
This thread has more details.
This french.stackexchange.com thread also looked at the question.
And the "ultimate" reference is here.
deleteand it told me it did not recommend doing so since it deprived future readers etc etc. I figure we have the option to "close as duplicate" for a reason. I only ever delete if I answer the question for myself before anyone posts an answer. – temporary_user_name Mar 16 '17 at 06:55