What is a "knot"?

Taken from the online version of the "GIA Diamond Dictionary":


knot

(1) Included diamond crystal oriented differently from the
larger diamond crystal which is its host. When such diamonds
are sawn, the knot may cause problems and slow the sawing
process because it often presents a harder cutting direction.
After polishing, a knot may stand slightly higher than the
surrounding surface.

(2) That section of a twinned crystal where the grain differs
from that of the main mass. Also called a naat.

-Tim

I will try an analogy:

A knot (also knat in Belgian I think) is like a knot in a piece of wood - so when you saw or sand it you are working end grain which is much harder. The result with wood is the knot will satnd up just like the knot in the diamond as O has explained from the gIA definition.

The knot arises because for some reason like change in temp / press or supply of carbon etc the diamond decided to start growing a crystal in another direction. This is called twinning - the growth of another crystal - usually in a 180 degree orientation on the same plane (the resulting crystal is a flat triangular outlined thing called a maccle that are often used to cut trilliants).

it is also possible for one diamond to grow faster than a neighbour and swallow it

Thank you Tim and Cut Nut for your helpful explanations! I was wondering, if the knot is an inclusion in a VS stone, what would it look like- would it be dark/light? Thank you again.

if you were really lucky it might be a pink diamond inclusion that would be a collectors specimen. It could be black too, but 99.9% are white and hard to see. If the stone is a VS then it is a VS - end of story - no reason why a stone with a VS naat should be a problem.