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.