I found the expression in the following phrase:
なんでも猟師が発見した石は、蝦夷の言うところによると、こんじんさまの怒りの気なのだとか。 それを掘り返すなど、望んで祟りを招くに等しいと.
I googled it and although I didn't find a dictionary entry there were many results.
気【き】 ("qi") means something like "energy", "force" or "aura". 怒りの気 usually refers to that dark aura emitted from a mad person.
See: Possible meanings for "気を巡らせる"
Of course a stone is not aura itself, so we don't usually say 石は怒りの気だ. Instead, we say 石には怒りの気が宿っている or 石には怒りの気が込められている. I don't know why this person said 石は怒りの気だ. Maybe the author made a mistake, or maybe it's highly "condensed" aura that looks almost like a stone?