Osmium tetroxide.
Osmium tetroxide is extremely poisonous and volatile, so if you so much as lean over it, it can severely harm your eyes. Fortunately my sample is sealed in a glass tube inside a protective plastic outer tube. Source:Tryggvi Emilsson and Timothy Brumleve Contributor:Tryggvi Emilsson and Timothy Brumleve Acquired:12 November, 2002 Price: Donated Size: 0.2" Purity: <20%