Internal graining is lines, angles or curves inside a diamond caused by irregular crystal growth. At 10x they can look whitish, colored or reflective, or lower the transparency.
In more detail
It comes from irregular crystal growth, not from a foreign crystal. GIA's 1997 moissanite study lists graining among the features that a diamond can show.
On a grading report
Drawn in red on the clarity plot of a full GIA report and named in the key to symbols. A Dossier has no plot but can name it in its list of up to four.
Related terms
- Surface graining: Surface graining is lines on the surface of a diamond, caused by irregularities in its crystal structure. It is like internal graining, but on the surface.
- Grain center: A grain center is a small, concentrated area of crystal distortion inside a diamond. It can be white or dark and can look like a thread or a pinpoint.
- Twinning wisp: A twinning wisp is a series of pinpoints, clouds or crystals that forms in a diamond's growth plane. It comes with crystal distortion and twinning planes.
- Inclusion: An inclusion is a clarity characteristic inside a diamond, or one that reaches the surface from inside.