Pyrite

Pyrite are both equippable items and NPCs in Magical Starsign and Magical Vacation. They are said to gain conciousness at 12mm.

Biology
Pyrite are silver cubes with no limbs. Their main method of movement seems to consist of one rocking back and forth. Each one has a face that resembles a three-prong outlet, with an orage glow coming from inside.

Behavior
Pyrite are very eccentric but vary greatly in other behavioral regards. Each pyrite seems to want nothing more than to join the player on his/her journey, even if that only means being sold for quick cash.

In Other Games
Pyrite are a trophy that can be obtained randomly in Super Smash Bros. Brawl

Trophy Description
"A strange little person living inside the stone giant on the earth planet, Erd, in the town of Uponisbak. You can talk to Pyrites and equip them like accessories, but they provide no real benefit in that sense. You can, however, sell them at a shop for a considerable price, proving their worth as a valuable asset when short on cash."

Trivia

 * In Super Smash Bros. Brawl, the trophy description shows that Pyrite only appeared in Magical Starsign, when they also appeared in Magical Vacation.

This is also the case with the Traveling Putty trophy.