Cesium is perhaps the most sought after element for those looking to complete a set of the periodic table. That's probably because, like gallium, you can melt it in your hand. Except you wouldn't do that because you would melt your hand off, too, in a strangely beautiful but all too tragic purple flame. However, holding the cesium safely with a little glass wall in between is another story. Much prettier than gallium, the brassy color and the sheer difficulty of locating the stuff heighten the appeal and wow factor.

Cesium metal ampoule with one gram of 99.99+ purity embedded in a 2x2 inch (50x50mm) block of crystal clear Lucite acrylic.