Knot as represented on GIA report
What is a Knot?
‘KNOT’ to sound overly alarmist here (I couldn’t help myself), but knots are bad news.
Knots are caused when a 'crystal' reaches the surface of a diamond. The difference between a knot and a crystal though is that a crystal rarely distorts the stone's shape or causes durability issues.
Not only are knots usually pretty visible within the stone (and it mightn’t even take a magnifier to see them either), but they also negatively impact the overall durability of a diamond.
This is an extreme example, but still. Knots can’t keep to themselves. They widen. They fracture. They crack. If the remaining crystal falls out, the knot can leave a huge cavity behind. Trust us, just avoid them.