What color is it?: As you can see above and below, this is a true synthetic opal with colors that closely emulate natural opal.
What is the story behind this gemstone?: This is a Gilson Synthetic Opal. The process used is just like a natural opal, with silicon spheres being generated that line up like soldiers in a straight line formation. Just like the natural counterpart, this has the effect of producing a diffraction grating of light into the spectral colors or refraction. The spheres are then surrounded by a material that is strong enough to withstand cutting and polishing to form this synthetic opal. It should be noted that materials other than silicon can be used to make these gem materials, but only silicon based material can properly be called synthetic opal.
Here’s the rest of the story on this synthetic opal……
Chemical: Si02 (silicon….glass)
Formation: According to Webster in Gems (Butterworth-Heinemann, 1997) the formation is by dispersing an organic silicon compound in an alcohol-water mixture. When ammonia or similar mild alkali is added to the mixture, silica spheres occur, which are then allowed to settle into the above referenced rows creating the diffraction grating effect of opal.
Crystal System: Amorphous
Unusual Properties: Lizard skin effect
RI: 1.450 + –
Optical Character: none
Hardness: 6 + –
Specific Gravity: Average 2.15
Special Identification Properties: As shown above and below, the Gilson Opal has a diagnostic lizard skin effect as seen in the photographs. This is easily seen in a 10x loupe, and is diagnostic for a Gilson Synthetic Opal.
Primary Test: Inspection with a 10x loupe and light source
Diagnostic “lizard skin” effect of Gilson Synthetic Opal
Secondary Test: None needed if you own a loupe.