The value of Australian opal can vary significantly based on several factors:

        1.      Type of Opal: There are several types of opal found in Australia, including black opal, white opal, boulder opal, and crystal opal. Black opals, particularly from the Lightning Ridge area, are often the most valuable.
        2.      Brightness and Play-of-Color: The more vibrant and varied the play-of-color (the spectral colors that shimmer and shift as the opal is moved), the more valuable the opal.
        3.      Pattern: Patterns like Harlequin (a mosaic-like pattern of colored patches) can be particularly valuable. Other patterns like pinfire, broad flash, and rolling flash also influence the opal’s value.
        4.      Size and Thickness: Larger opals with a good play-of-color are generally more valuable, as are those with a thicker color bar.
        5.      Inclusions: Opals that are free of inclusions or cracks are more valuable.
        6.      Body Tone: For black opals, a darker body tone (background color) is often more valuable.
        7.      Treatment: Natural opals are more valuable than treated or synthetic opals.
        8.      Origin: Even within Australia, the origin can matter. For instance, high quality black opals from Lightning Ridge can command higher prices than those from other regions.

In general, the price range for Australian opals can start as low as $10 per carat for common white or crystal opals with little play-of-color, and can skyrocket to over $10,000 per carat for high-quality black opals with a vibrant play-of-color and an appealing pattern.