Australian Opal is by far one of the hardest gemstones to value, as the price isn't exactly related to the clarity or tone of color in the way most gems are. Opal can range from under $10 a carat to over $15,000 a carat, which is determined by these main factors;
1. Play of Color
6. Cabochon Shape
7. Sand inclusions/webbing/crazing/polish
8. The Market
These are the main factors in determining the value of opal, and due to all of these factors pricing opal can be a headache for even experts in the field.
Play Of Color
Play of Color in opal is categorized by the shifting color that makes opal so magnificent. This phenomenon is broken down by color, pattern, brightness, and directionality. The color of these bright flashes is important to the value as it changes by rarity. Blue is actually the most common color in opal, making it the least valuable while red is the most valuable as it is the rarest. A black opal with a vibrant red flash can be worth more than ten times that of one with a blue flash.
Bodytone is another important factor in opal, which is rated on a scale of N1 (Black Opal) to N9 (White opal) and also includes crystal opal which is another factor determined by the bodytone.
White opal has a bodytone of N7-N9 (Shown on the scale below). White opal with noticeable Play Of Color can range from $10.00 USD per carat to over $500.00 per carat.
Next is Dark Opal, ranging from N5 to N6 on the chart. The darker bodytone is more rare making the value range from around $30.00 to $4000.00 per carat. In both dark and black opals the color shows up much more vibrantly, and combining that with the rarest patterns in opal, the value can skyrocket.
Black opals ranging from N1-N4 can range from $50.00 per carat to over $15,000 per carat in rare cases. One famous crystal opal known as the "Virgin Rainbow" is 72 carats and worth around one million dollars USD. Check out the guide below to learn more about the bodytone and brightness scale.
Crystal Opal is classified by its translucency rather than just bodytone. With crystal opal, the clearer and less opaque stones with bright color are prized the most, with a range that can be anywhere $10.00 a carat to $15,000. Crystal opals can also range from N1-N9 on the bodytone scale, meaning they can also be black opals, classified as "black crystal opals" where they have a dark tone but light can travel through the stone if illuminated from behind.
The brightness of an opal is determined by how much light is refracted, and range from looking quite dim even under direct light to looking as if they are glowing even under dim light. This can greatly effect the value, as an opal with a brightness of 1 out of 5 is worth a mere fraction of an opal with a 5 out of 5 brightness. Brightness can take a black opal from $50 USD a carat to over $5000 a carat alone. Brightness is also effected by the directionality of the color, as from some angles the color may not show at all and others it might be extremely vivid. In this case the evaluator with rate the brightness by splitting the difference based on how often the color shows from every angle.
The Virgin Rainbow
This amazing gemstone is valued at over $1 million dollars USD, due to its incredible brightness that almost seems to glow in the dark. It weighs 72 carats, making it about $14,000 per carat. Many consider it to be one of the best opals to ever be unearthed.
The Virgin Rainbow opal from the South Australian Museum opal exhibition. (Credit: South Australian Museum)
Eric The Pliosaur
Many know opal for the fossilized squid known as Belemnites, but did you know that it can replace many other skeletons as well? One of the best examples of this is an opalized dinosaur which was unearthed in 1987.
The Andamooka Opal
The Andamooka Opal is a gemstone that was gifted to Queen Elizabeth II in 1954 when she took a trip to Australia. This 203 carat crystal opal is set in a diamond studded necklace with a matching smaller pair of opal earrings as well as two more that were made into Cufflinks for Prince Philip.