Opals really are a mixed bag of gemstones. Just some of the varieties include white opals, black opals, fire opals, pink Peruvian opals, hyalite opals and I could go on for quite a while yet.
Boulder Opals are one of the better known gemstones in this family. They are distinct from most other opals by still being connected to the rock in which they formed.
This means that the thin slivers of precious opal have a substantial foundation so it is much more durable and the dark rock is a perfect background for the vibrant play-of-color.
Boulder Opal Colors
There is no such thing as a typical Boulder Opal color. Every gemstone is different in both shape and color with every color of the rainbow a possibility. Not only can Boulder Opals feature all colors but as the stone moves other colors can flash or dance before your eyes.
The precious opal material that forms in cracks and crevices within the host rock is made up of tiny spheres in which light can bounce around creating the dazzling colors.
Larger spheres bring out the red colors while smaller spheres show up as blue. Large spheres are rarer so any Boulder Opal showing colors such as red or orange - the ones at the top of the rainbow - will be more expensive than the blues and greens found at the bottom.
Read more about gemstones colors here
Boulder Opal Species
Boulder Opals are just one of many types of opals found around the world. Some have the famous play-of-color while others are a single color but all are fascinating gemstones.
Just a few of the more well-known ones are:
And there are many more besides.
Boulder Opal Price
Like most gemstones, it is the color of the Boulder Opal that is the number one consideration when appraising its price. However, there are a couple of extra considerations to bear in mind with this stone.
There is the coverage - a gemstone that has a large area of precious opal spread over the surface will get a higher price than one with a few spots here and there.
A contrast between a dark background and a bright color can increase the value of the opal.
As we mentioned earlier, some colors are rarer than others and a simple rule is to work your way down the rainbow with the red at the top being the most expensive and the purple at the bottom being the least expensive.
This is a very basic rule which can vary from stone to stone with the coverage and contrast aspects to bear in mind.
Carat Weight
Boulder Opals are precious opal material still connected to the base rock so they tend to be quite large gemstones. They can also be irregular shapes to incorporate as much of the naturally occurring opal as possible.
Pricing Boulder Opals on carat weight can be a little tricky as there is often a lot of ironstone or sandstone left after cutting and polishing. It may be a very thick and heavy stone with just a thin veneer of colored opal on the front.
It is best to choose your Boulder Opal based on physical size - the length, width and height - rather than carat size. As a very rough guide, Boulder Opals can be anything from $2 to $15 per carat for basic colors up to $50 to $800 per carat for gemstones with outstanding colors, depending on color, coverage and contrast.
Treatments
Generally, Boulder Opals are a completely natural gemstone with no treatment other than cutting and polishing.
As we have said, the contrast between the opal and the rock background can increase the value so there have been cases of the base rock being smoked or soaked in sugar to darken up the body but this is not very common in Boulder Opals and happens more with Black Opals.
Sometimes the precious opal can come loose from the rock backing and can be reattached with glue or resin. This would be difficult to spot unless a sudden impact or high heat breaks the seal but we are not aware of this being a serious problem.
Any treatment received by any of our gemstones is clearly disclosed.
Where are Boulder Opals found?
Basically all Boulder Opals come from central Queensland. This may not sound that impressive but it is an area about the size of California and home to about 200,000 people (and lots of kangaroos, rock wallabies, goannas and spiders).
What jewelry is Boulder Opal suitable for?
Boulder Opals have a rating of 5.5 to 6.5 on Mohs hardness scale. This would usually make them a little bit fragile for many jewelry items and not suitable for daily wear, however Boulder Opals are still attached to the durable rocks they formed in so are much tougher than the rating would suggest.
Large and striking Boulder Opals cut into interesting odd shapes can help create wonderful and unique jewelry items, especially pendants, brooches and earrings where durability is not such an issue. Boulder opal rings in protective settings can be particularly striking items of jewelry.
Birthstones and Anniversaries
Boulder Opals are the birthstone of October and would make an ideal gift for anyone celebrating a birthday in that month.
A Boulder Opal is the traditional gemstone gift for the 14th wedding anniversary.
