Alchemical Symbolism in the VMS

[Paris]

That's right : these cubes symbolize the philosopher's stones.

Cinnabar = HgS = Mercury (Hg) and Sulfur.
In fact, there are also impurities.

The river we see in the back is a river of mercury.
The philosopher's stone needs mercury (the metal), sulfer and a third element (salt - not the common salt).
Many alchemist designate mercury and sulfur as primary (materia prima).