So now you know how to tell the difference between natural solid and man-made opals, we need to talk more about location, location, location! But why, I hear you ask. Well because your opal will have different characteristics depending on where it was mined.
Most Australian opal is considered stable because they have a lower water content (3 to 10%) and is less likely to crack - especially once put through the pressures that come with the cutting process. Also natural solid Australian opals will NOT be effected by immersion in water, oil, or any other natural substances. All Australian opals are sedimentary in origin and more importantly are Non-Hydrophane.
On the other hand opals from other regions, like Ethiopia, can be of a volcanic origin and more prone to cracking. Ethiopian opal can be of 2 types: Hydrophane or Non-Hydrophane. Most recently mined Ethiopian crystal opals are Hydrophane opals. This means while they are dry they will display brilliant colour patterns, however once immersed in water their colour will become dull or disappear. So while wearing a Hydrophane opal on your skin while sweating (and who doesn't?) in turn will result in the colour fading. In other words the hydrophone opal will absorb the water from your skin. To buy Ethiopian opal is absolutely fine as long as the seller declares the origin of the opal and whether it is Hydrophane or Non-Hydrophane. Of course the price should be reflected by both origin and type. Believe me, Hydrophane opal can look a million dollars and many buyers have been caught unaware of the differences between them.
So in summary, ask lots of questions before you buy your next beautiful opal!