Iodine


Iodine Solid Pieces
Source:  Found, Lab Cleanout
Purity:  99.95%

These pieces of Iodine clearly sublimate, or change directly from solid to gas, and the vapor deposites on my desk as a brown stain that is impossible to get out.  It also emits the least caustic of the highly detectable, characteristic halogen odors.  Even holding it in your hand for a second turns it brown and makes it stink.