Opals are graded as Top Grade AAA when they are solid, large, have very good fire, and with a size range of 2.5 and above. Smaller pieces that range between 1.8-2.5 grams occasionally will qualify to be Top Grade AAA depending on their fire and solid shape.
Polished
Rough
Top Grade
Opals are graded as Top Grade when they are solid, very good fire, and with a size range of 1 to 2 grams.
Polished
Rough
Medium Grade
Opals are graded as medium grade when they have relatively good fire but may have some minor cracks. At the same time, a medium grade opal may be crack free yet not have great fire.
Polished
Rough
Specimen
Specimen opals are generally large with very good fire. They either have cracks or dirt inclusions which is the reason they are not Top Grade AAA. Some specimens are solid enough to be polished, and in some cases they are good only as a specimen and not recommended for cutting. .
Polished
Rough
Low Grade
Opals are graded as low grade when they have a large amount of dirt inclusions and/or cracks, similar to specimens yet smaller in size. Low grade opals may still have brilliant fire patterns.
