There are several types of opals so I listed the three you asked about and two additional types, Black and Crystal Opals.
Are artificially made and although their structure is very similar to the structure of precious opals, their value is (from obvious reasons) much less than the value of the real “thing”.
Synthetic opals usually display a very distinctive snakeskin pattern and they show brighter colors than natural opals. The spots of color are larger but they interact with light in a very similar way to natural opals. They also contain a fair amount of silica (usually around 70-75%) which is impregnated with plastic. Synthetic Opals look good and appeal to some but cant replace what Mother Nature creates
Boulder/ Natural Opal
This type of opals are not as known and valued as black opals but their stunning appearance and in many cases dramatic combination of vibrant colors makes boulder opals eye catchers and puts them on the list as a second most valuable and sought after type of opals. Boulder opals are formed in cracks of ironstone boulders. They are found only in the state of Queensland, Australia.
Because boulder opals are very thin, they have to be cut out together with the ironstone on the back. This attachment gives them dark body tone and appearance very similar to black opals.
At a first glance, boulder opals also might be mistaken for a doublet. The main difference is that the backing on boulder opals is completely natural.
Lab Grown or Lab Created Opal
These terms generally refer to polymer-impregnated opals, which are 70-90% silica (from which natural opal is formed) and 10-30% resin. Lab created opals exhibit fire play resembling the finest opal at a small fraction of the cost.
Are the rarest and at the same time the most beautiful of all types of opals. If the opal is “Queen of Gems” than the black, opal is certainly “King of Queens”. No wonder black opals are also the most expensive and sought after type of opals. For people buying opals as a good, solid, long-term investment, black opals are definitively the ones to go for
Their unique, elegant and most of the times breathtaking appearance comes from their dark body color. The color can range from dark grey to deep black and it is a direct result of carbon and iron oxide trace elements, which are naturally incorporated into black opal’s structure.
Is a term used in relation to any type of opal with a transparent or semi transparent body? They display their colors in the same way as the other types of opals but the transparency of their body gives them a different and unique appearance that many people find more appealing. Good quality crystal opal is not as valuable as black opal but its price is usually very close to the price of boulder/natural opals.