clarity (purity)

The purity of diamonds can be rated by carefully observing its internal imperfections, the so-called "inclusions"; inclusions may be of different kinds, from internal crystals embedded inside the diamond to real cracks.
The more the stone is inclusion-free the more it is worth and, vice versa, the more such inclusions are evident the lower the stone value
The Gemological Institute of America defined an international purity scale for classification purposes.

IF
Identifies a stone with no inner inclusion detectable at 10x magnification.

VVS1 / VVS2
Identifies a stone with extremely small inclusions which can very hardly be seen at 10x magnification.

VS1 / VS2
Identifies a stone with very small inclusions which are visible at 10x magnification.

SI1 / SI2
Identifies a stone with small inclusions which are easily visible at 10x magnification.

I1 / I2
Distinctively identifies noticeable inclusions which are visible to the naked eye.