Puella Magi Madoka Magica the Movie Part 1: Beginnings Things

Black thorns from which witches are born from. Once planted, they will soon form into a barrier hidden from normal sight while the witch matures. When a witch is defeated, the remaining Grief Seed may be used to restore magical power to a Soul Gem.

A gem that holds a magical girl's power, which its user can use to transform. The gem glows whenever a witch or one of its familiars is nearby.