how do diamonds get feathers?

[radiantquest]

i am interested to know exactly what happens when the diamond is forming that causes a feather

 

[Lorelei]

What bascially happens I have copied from one of John Pollard''s posts below, hope this helps.

"A feather is a fissure inside a diamond. It''s often caused by a crystal inside the diamond that expanded millions of years ago when it formed, or can be any space between two parallel planes in the diamond. If it doesn’t break the surface or run for a long way it likely poses no problem; remember that a diamond will never be exposed to the extremes of pressure and friction it endured during the cutting process in everyday wear... On the other hand an open feather can pose a durability risk, depending on its size and position.

Feathers are very common in SI clarities and should be considered on a case by case basis. Some are prongable but with others it may not be advisable depending on size and position. If there is a question examination by a knowledgable appraiser or other expert can provide a definite answer.

While on the subject, questions about feathers often come hand-in-hand with questions about chipping. Something we''re in the habit of reminding people is that diamonds have natural cleavage planes. A knock the wrong way, especially at the girdle, may cause any diamond to chip/incur damage - feather or not. This is why having a good insurance policy is important for even the most flawless diamond. "
John