You’ll find me in Mercury, Earth, Mars, Jupiter, Saturn and Uranus. But never Neptune, or Venus. What am I?

I seldom seem like very much, until there’s twelve of me.

Found in fever, but never in temperature. When this takes effect, the answer becomes clear and direct. Though chance may offer alternatives, only one choice persists.

A maze, labyrinth, riddle, or box, I challenge your mind through passages twisted or plain. Each may take on my name, turning thought and confusion into a game.

I have no soil, yet plants can grow, I hold no crop, though seeds I sow. I stretch as far as light can bend, With north and south, but neither end. Battled on by minds or men, I hold position now and then. I can be seen through glass or screen, Or felt where magnets lie unseen.