Those letters and numbers are the Gemological Institute of America’s (GIA) gem clarity grading codes. Jewelers and gemologists frequently use this system. To understand what the codes mean, you’ll need to know what the codes stand for and the clarity type of the specific gem.
Clarity is one of the Four Cs of gemstone grading. A gemstone’s clarity grade indicates the relative absence of inclusions (materials trapped inside the gem), fractures, and blemishes (surface imperfections) that affect its appearance and structural integrity.
Of course, other factors can impact a gem’s appearance and structure, most notably the cut. However, clarity covers factors that are part of the physical makeup of the gem itself. A poor cut or polish are things people have done to the gem.
Opaque and translucent gems have somewhat different clarity standards than transparent gems.
Colored gemstones can have the following clarity grades:
The numbers for SI and I grades indicate increasing degrees of inclusion visibility and structural impact.
You might encounter stones with clarity grades of Dcl on the market. Dcl (déclassé) means a stone doesn’t have the transparency or durability for faceting. However, Dcl stones may be used for cabochons, beads, or carvings if they’re structurally intact.
Diamonds (and only diamonds) can have clarity grades of F and IF. These mean “Flawless” (no inclusions or blemishes visible with a 10X loupe) and “Internally Flawless” (like Flawless, but may have blemishes visible with a 10X loupe). There are other differences between diamond and colored gem clarity grades..
A gem’s clarity code won’t tell you the whole story. You also need to know its clarity type.
Some gem species frequently contain many noticeable inclusions. Other typically have few inclusions. This varies due to the many ways gemstones form underground. The GIA has divided colored gemstones into three categories or types: I, II, and III.
The following table divides some popular colored gemstones into these clarity types.
| I |
Usually eye clean
Almost always included
Chrysoberyl, yellow and green
Corundum, all (ruby, sapphire)
Quartz (amethyst, citrine, ametrine)
Tourmaline, all but green, red and watermelon
Zircon, all but blue and colorless
Tourmaline, red and watermelon
Note that some gem species, like beryl, quartz, and tourmaline, fit into different clarity types, depending on the color variety of the specific specimen.
“Eye clean” (or “eye clear”) means the gem has no evident flaws visible to the unaided eye when viewed from a distance of about 6” to 12”.
Now, you’re ready to interpret clarity grading codes. The grades mean different things according to the gem clarity type.
|VVS||Minute inclusions, difficult to see under 10X. Eye clean.||Minor inclusions, somewhat easy to see with 10X. Usually eye clean.||Noticeable inclusions under 10X. Usually eye clean.|
|VS||Minor inclusions, somewhat easy to see with 10X. Usually eye clean.||Noticeable inclusions under 10X. May be eye visible.||Obvious inclusions with 10X. May be eye visible.|
|SI1||Easily noticeable with 10X. Slightly visible to the unaided eye. Usually low relief.||Obvious inclusions, large or numerous under 10X. Apparent to unaided eye.||Prominent to unaided eye.|
|SI2||Easily visible to the unaided eye. Usually low relief.||Obvious inclusions, large or numerous under 10X. Very apparent to unaided eye.||Very prominent to unaided eye.|
|I1||Moderate effect on appearance or durability.|
|I2||Severe effect on appearance or durability.|
|I3||Severe effect on both appearance and durability.|
You’ll need to know the following definitions, too:
So, for example, an SI1 score for a tanzanite, peridot, or emerald could mean very different things!
Usually, gems with greater clarity — with fewer inclusions and blemishes — are considered more valuable than gems of the same species with lower clarity, all other properties being equal. For some gems, like rubies, the difference can be significant. For other gems, the difference may be minimal.
On the other hand, some gems, like demantoid garnets and Oregon sunstones, are actually prized by collectors for having rare or aesthetically pleasing inclusions.
However, just because a gem has a type II or III clarity grade doesn’t automatically mean its value is lower than a type I gem of the same clarity grade. For example, the prices of emeralds (type III) and sapphires (type II) can greatly exceed those of most type I gems.
From the International Gem Society