A feather is a small fracture within a diamond’s internal structure. Depending on the viewing angle, a feather can be almost invisible or catch on to light and look like a small white feather within a diamond. Rarely feathers may have a grey or brownish colour, and they are noticeable to the naked eye.
Massive feathers can cause durability issues, especially if they reach the surface or the girdle, which is why such diamonds should be avoided.