Guide to Opals

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Kinds of Opals include the following:

Natural opal

• Natural opal is any opal that has not been treated or synthetically altered.
• It has an ironstone backing with base tones in colorless, white, various shades of gray, and black.
• It can be opaque, translucent, or transparent.
• Transparent or very translucent opal with sharp color clarity is referred to as crystal opal.
  

Light opal

• Light opal has a base tone that ranges from colorless to medium gray.
• It is sometimes called white opal.
• It makes up the bulk of precious opal.

Black/dark opal

• Black or dark opal has a dark body tone that shows the play of colors within.
• It can be crystal or opaque.
• It is more expensive because of its clarity, color, and pattern.

Boulder opal

• Boulder opal is a precious opal with an ironstone host rock bonded to it naturally.
• It usually has a thin vein of precious opal only.
• It can be black, dark, or light, depending on the appearance of the host rock and the angle of view.

Matrix opal

• Matrix opal is diffused with infillings.
• Its pore spaces are chemically treated to enhance its color.

Composite natural opal (doublet/triplet)

• Composite natural opal is a combination of natural opal and artificial veneers.

Colors:  To get the finest opal in terms of color, choose one with a variable interplay of colors in its internal structure. It should have packed silica spheres from 150 to 300 nm in diameter to produce interference and diffraction when light passes through it.

Translucency:  Look for a translucent opal for more refraction and interplay of colors under light.

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Solonial Opal
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