Opals are considered to be one of the seven sacred stones of the Cherokee people.

it depends upon what kind of opal you have what it can do:
white opal, sunflower opal,
black opal, boulder opal, sonoma opal, sun opal,
 mountain opal, jelly opal,

fire opal, cacholong opal, or California opal.
Each work differently.

Opal Carries Moon and Sun Energies
Opals are formed from balls of silica.
This silica has different levels of depth and density and holds water as well.
 That is where the "rainbow" colors come from.
The opal is used for helping one that doesn't want to appear in the front or
allows you to
 "fade into the background."
Or to be less noticed.

 A stone of happy dreams and good changes.
The opal can be used to help one open their "mystical" side.
 Gives you understanding of the Higher Powers.
This stone carries both the sun and moon's energy.
It is basically a moon's stone or female energy
but has it's flash of male energy in the iridescent colors
and carries the sun's energy.

 These flashes encourage intuition and insight.
These flashes also represent an "inner fire"
that gently stimulates you towards the Spiritual realms.
 Can be used during astral travel but is NOT a powerful stone for astral travel,
 the energies are more subtle. Opals should be moistened often by a natural oil or water.
If all the water evaporates out of the stone it will become fragile and break.
The opal is tied to our emotional side.