Osmium tetroxide is the chemical believed to be at the centre of an alleged bomb plot foiled by UK and US intelligence agents.
It is thought the supposed plan involved detonating an explosive device and the compound.
Osmium tetroxide is used by scientists to stain materials and as a catalyst - something that speeds chemical reactions.
It is also a toxic substance with corrosive effects on eyes and skin, making it dangerous to touch or inhale.
And it would also have the ability to cause panic if released in a closed environment.
But given its high cost and volatile nature, scientists say it makes an unlikely ingredient for an effective "dirty bomb".
What is osmium tetroxide? - BBC NEWS
The feasibility of using a bomb to disburse OsO4 is highly suspect. When heated OsO4 rapidly decomposes to OsO2, which is effectively a rock.
CNS - Osmium Tetroxide - a New Chemical Terrorism Weapon? - Apr. 13, 2004 - Research Story