* I removed the density from the database. After a long discussion we (BlueObelisk) agreed that it is a compound property and thus does not belong into Kalzium.

Example: Carbon exists at least in three forms: graphite, diamond and buckyballs (Fullerene).

This means I need at least three (3) values for the density as all three forms of carbon are "carbon". The same applies for S, P and many many other elements.