1. Type --- natural solid opals and boulders are considered valuable. Black opals are the rarest and enjoy highest prices in the market.
2. Brilliance --- it is the most important factor in valuing opal. Opals with brilliant colours attract at once our attention and their price shoots up as their intensity increases.
3. Transparency --- it is applied mainly in light opals, of which crystal opals with good brilliance are very highly priced.
4. Body colour --- black opal is in general more expensive than light opal. The blacker, the better. Its profound mystery of "play of colours" is easily enhanced and is very attractive.
5. Diffracted colour --- there are red, orange, yellow, green, blue, indigo and violet. As most of the silica spheres are about 0.00025mm and produce blue-ranged colours. Red is very rare but blue is very likable in many countries.
6. Pattern --- although opals with distinct patterns are collector's such as harlequin, ribbon and peacock tail, pinfire and other small patterns are still in great demand.

The factors mentioned above are just simple guidelines and it is necessary to find your personal preference. Try on to see if it suits you!

1. Opal looks brittle, Does it break easily?
   Opal is much harder than pearls and is about the same hardness of jade and some other precious stones. Opal is a gemstone and should be taken with great care all the time. You would not wear it washing dishes or playing tennis.
2. Is opal valuable? Can it be collected?
   Opal is recognized as the national gemstone of Australia and many royal family members in Europe are opal lovers. Gem quality opal is very scarce and is sought after. Many Europeans and Japanese love collecting it as its price has been climbing up.
3. How should I start with my first pieces of opal jewellery?
   First, it is advisable to find a trustworthy jeweller as appraisal of opal is quite specialised and ordinary jewelers may not be able to answer all your questions. Second, start with crystal opal as you will have a better range of choices. Third, see more opal jewellery and ask more about the qualities of different opals. Better understanding, wiser buying!