Most Diamonds contain tiny marks, known as inclusions, which make each stone unique, like a finger print. The inclusions don't necessarily weaken the stone and when they don't interfere with the passage of light they do not affect its beauty. The fewer and smaller the inclusions, the more valuable a diamond will be.
The grading starts at FL which is a completely flawless and extremely rare diamond. The GIA clarity scale chart below shows the different grades of diamond clarity. For grades FL to SI, a diamond's clarity grade has an impact on the diamond's value, not on the unmagnified diamond's appearance
|IF||Internally flawless||No internal flaws, but some surface flaws. Very rare.|
|VVS1 - VVS2||Very Very Slightly Included||Minute inclusions very difficult to detect under 10x magnification by a trained gemmologist. VVS1 is slightly cleaner than VVS2.|
|VS1 - VS2||Very Slightly Included||Minor inclusions only visible under 10x magnification. VS1 is slightly cleaner than VS2.|
|SI1 - SI2||Slightly Included||Inclusions easy to see under 10x magnification but usually not visible with the naked eye. SI1 is slightly cleaner than SI2.|
|I1 - I2 - I3||Included||Inclusions visible with the naked eye.|