Precious Opal’s vibrant, illuminating colors and artistically unique patterns make this gemstone not only rare, but truly fascinating. No other gemstone compares with the multitude and phenomenal “Play of Color” that a single Opal can possess.
Often referred to as the "Queen of Gems", Opal throughout history has been surrounded by mythological lure. From the Roman aristocrats to the Aztec rulers, and eventually gracing the writings of Shakespeare, Opal has captivated a world of an audience!
What is the nature of Opal?
Opal has a chemical composition of hydrated silicon dioxide(SiO2-nH20).
Both the common and precious opal varieties are comprised of
nanometer sized silica spheres and a water content ranging between 3-10%, with some stones
containing up to 20%. The Specific Gravity of Opal is 2.15 (+.08,-90), dependent on the density of mineral content. It has a Refractive Index 1.45 (+.020,-.080) and measures 5-6.5 on the Moh’s
Scale of Hardness
What causes “Play of Color” in Opal?
The rare occurrence and phenomenal "Play of Color" observed in Precious Opal is derived
through perhaps accidental perfection ; the incidence of a three dimensional grid work of silica spheres.
By viewing the stone at different angles, opal can display a rainbow of colors through means
of light diffraction produced throughout and around the silica spheres. The size, stacking and
concentration of the spheres will indicate the various colors and patterns
observable in the stone.
From the famous Black Opal lightning Ridge fields in New South wales to the Boulder and Yowah varieties from Queensland, and the underground of Cooper Pedy's white opal; Australia accounts for the majority of the worlds Opal production.
Australian Opal grades (N1-N9) are based on the color of the 'potch', the natural body tone of the opal.