Harlequin opal is precious opal in which the colours shine as patches or spangles. The patches are regular with definite boundaries, and are distributed in a way that forms a mosaic composition (not to be confused with mosaic opal). The term originates from the costumes worn by harlequin clowns. Many people believe that harlequin refers only to the extremely rare ‘chequerboard’ pattern. This is most likely a rumour spread by knowledgeable dealers in the early days of the Australian industry, in order to dupe miners and turn a profit in Europe. In fact there are many different patterns which classify as harlequin, and the chequerboard pattern is in fact exceedingly rare.

Barry O’Leary’s definition of a harlequin opal is; “True precious opal showing a regular mosaic-like chromatic pattern in rounded, angular, or roughly square patches of about equal size, presenting a spangled appearance”.

Here are some of the many descriptive terms utilized to classify harlequin opals:

• Asteria Harlequin; a rare formation showing elongated colour units radiating outwards from a central nucleus.
• Blue Harlequin; any harlequin opal of any subgroup showing a pronounced colour play in the blue spectrum.
• Chequerboard Harlequin; exceptionally rare opal type showing regularly arranged, square-shaped units of colour.
• Cloverleaf Harlequin; units of colour forming a cloverleaf design, by having a central unit surrounded by a ring of outer units.
• Fish Scale Harlequin; a pattern of colour resembling a fish scale design.
• Flag Harlequin; a pattern of colour units resembling a three-cornered flagstone paving.
• Flagstone Harlequin; a pattern resembling the design or an irregular flagstone path.
• Floral Harlequin; a splashy effect of units which can be likened to the bright floral patterns of dress materials, or to bunches of flowers. Three or more units of colour, closely grouped, make up a flower. A very rare pattern.
• Green Harlequin; any harlequin opal with a pronounced green hue.
• Hexagonal Harlequin; a very rare pattern showing hexagonal colour units arranged together in an interlocking design.
• Palette Harlequin; a pattern with widely spaced units, similar to the layout of colours on an artist’s palette.
• Square Harlequin; squarish disjointed colour units are present in the opal pattern.