Solid (cabochon) – The opal is left in its natural state.  It is only shaped and polished on the cutter’s wheel.  If the gem is thick enough, most cutters prefer to cut it en cabochon.

Doublet –A thin veneer of opal,  with a dark backing of either black or grey silica material, or a thin slice of common opal cemented to the back of the opal.

Triplet –A slice of quartz may be used to cap the thin opal veneer to protect it from abrasion. This produces a three-tiered gemstone known as a triplet.

Because the doublets and triplets are made with glue, they have a tendency to separate if immersed in water.

Play-of-color – an optical phenomenon, due to the unique formation of the opal. All colors of the rainbow can be seen as the gem is turned this way and that.

The Description of Play of Color:

Harlequin Pattern: The rarest pattern, the colors are arranged in a diamond shape.

Floral Pattern:: The most common pattern – this covers a broad range of design and color.

Pinfire Pattern: Resembles differernt colored pinheads.

Palette Pattern: Resembles an artist’s palette.

Rolling Flash:
Usually consists of one color that travels across part or all of the stone as it is moved. Check out this black opal for an example of rolling flash.

Here are some terms the opal enthusiast will need to know in order to fully appreciate  the magic that is opal collecting!

Andamooka opal – a type of opal from Andamooka, Australia
Black opal – a rare type of genuine opal with a dark body color
Boulder opal – genuine opal in which brown host rock may be seen
Fire opal – opal with a strong reddish or orange color, mostly from Mexico
Harlequin opal – a very rare, genuine opal that has a “harlequin” pattern.
Jelly opal – a transparent type of opal that has a jelly-like appearance

Gilson opal – this is imitation or synthetic opal
Japanese opal – plastic imitation
Slocum opal – imitation

Opals are unlike any other gemstone in that they are composed of hydrated spheres of silica. These spheres give rise to the “play-of-color,” or “mini-rainbows,” which is an opal’s distinguishing characteristic.

Opals are typically cut flat or in cabochon – no additional brilliance will be uncovered by faceting. Opal is a fairly soft stone, 5.5 – 6.5 on Moh’s scale, so thery must be treated with care.

Opal is categorized based upon the body color – light or dark – and the degree of transparency. (The body color is its base tone, not the rainbow colors in the play of light.)

Crystal – when an opal is transparent or translucent. The play of color must be visible both on the surface and within the stone.

Jelly – when the color in a crystal opal is hazy.

Fire crystal – crystal or jelly opal with an intense, fiery orange color