What are Black Opals?
Black opal is characterized by a dark appearance which can range from dark grey to jet black. Australian black opals are considered the most valuable and widely known type of opal.
Black opals are different from other opal stones. They have carbon and iron oxide trace elements in them which gives it a dark tone. Because of their dark appearance, the rainbow colours in a black opal sets it apart from other opals. A black opal usually has a natural layer of potch left on the stone which gives the stone an extra dark shade as well as vibrancy. The colour of the potch compliments the darker shade of the stone itself.
Non-crystalline silica dioxide and water are mixed into fossils called Nobbies. The mixture is then streamed and pressurized into the cracks of stone for millions of years. These layers of silica within the stone give its transparency and locks in impurities to refract light.
Black opals are generally cut into oval shape but that mainly depends upon the shape of the stone. Sometimes, these stones are cut into freeforms or even teardrop to make the stone appear big in size. Black opals are generally cut with a low cabochon due to the opal colour bar often being much thinner in black opal than regular opals.
Now let’s see how black opals are graded.
Black opals gradation
These gemstones are graded according to the dark shade which enhances its richness colour prism. Nevertheless, the addition of silica content makes it very delicate and easily dulled in high intensity of heat.
Apart from this, black opals are graded in terms of pattern, brilliance and transparency.
- Pattern: The pattern scale is rated from “Good” to “Excellent”. Every pattern possesses a unique layering that comes in lines, bubbles and crosses.
- Brilliance: As we all know, the brilliance or dullness affects the amount of light which will be refracted by the stone. Keeping this point in view, no matter how many prisms a black opal may have, if it lacks brilliance, it loses its bounty.
- Transparency: One way to view a stone’s transparency is to look through it in light. Although these opals are black in colour, their transparency will aid in you seeing the deeper regions of the stone’s colour pattern. It also enhances the brilliance of a stone but it is not the sole factor which increases its brilliance.
How much do black opals cost?
Since black opals are becoming rare, their price keeps increasing. These stones are majorly used in jewellery and look stunningly beautiful when set in white gold and platinum in contrast to its lighter and opaque version.
The prices are hard to explain in numbers due to its rarity. However, you can always know the exact price from a trusted price.
Another factor when looking into the price of these stones is their cabochon. This defines how domed they are. The more domed a stone is, the more expensive it may get. A domes opal is reflected with a greater amount of light and allows colour to roll from all angles.
For more details, you can visit SFNCrystals to gain more information about these stones.