Sydney Wientjes; Block 1
Then Francium is perfect for your needs.
First of all, it is so rare that there are no actual pictures of the element in its purest form. Secondly, since it is the most reactive of the alkalai metals, it creates violent reactions that become explosive when combined with elements other than Uranium.
No one else will own this one-of-a-kind element (more than 22 minutes, that is!).
Here is a video of the reactions of the alkalai metals in water. The last one is Francium. Can you tell?
So, what are you waiting for? Come catch a glimpse of the scarcest and most uncommon element today!