The place where the sky and the sea meet is the edge of the world.
My anxiety is mixed with excitement.
After snatching my wallet, the pickpocket quickly blended in with the crowd and disappeared.
You know that 交ぜる means to mix and that the kanji means mix as well. So, this probably has something to do with mixing things. This word means to be mixed. This is when something is mixed but it's not mixed by you. It's just being mixed. Think of it this way - the じ in 交じる is Jesus, who just uses Jesus magic to mix something. So, you're not mixing it. It's just when something is to be mixed.
The reading is the same as with 交ぜる. So long as you know the ま portion of that word's reading, you'll be able to read this word as well.