When you look at something, say some writing, through a clear piece of calcite you see that the image is split into 2 which rotate around each other as you rotate the crystal.This is a physical property is a key to understanding it metaphysically.
Calcite encourages you to see things with a degree of separation, much like the watcher in meditation, so it can often defuse a stressful piece of conditioning and encourage clarity of thought.
As a cubic stone it can also use that clarity to construct better systems of conditioning.
Aragonite is a Tetragonal Calcite. The cubic shapes form partly inside each other resulting in a six sided flat topped crystal shape. These have a bit more of a spiritual direction.