15 Phosphorus (P)

atomic weight 30.97, melting point 44.1° C, density 1.82g/cc

Red Phosphorus medal by Metallium, Inc. Photo used by permission.
Diameter 19 mm, 0.8 grams, xx.x% pure (mixed with binder). $55 on 7/16/2009.

White Phosphorus version of the same. The white allotrope is poisonous, very reactive, and unstable. Over time, with heat, it will turn to red phosphorus.