From the case:
Gadolinium

Pure (99.95%) amorphous gadolinium, ~12 grams, 2 × 1.5 × 0.5 cm, cast in acrylic glass.
Author: Jurii
Original file: https://commons.wikimedia.org/wiki/File:Gadolinium-2.jpg
Modifications: none
License: Creative Commons Attribution 3.0 Unported license