Naat — A Twinning Knot in Diamond
Naat — A Twinning Knot in Diamond
The Afrikaans trade term for a localised lattice distortion that scatters light and lowers clarity
A naat is a twinning anomaly or 'knot' in a diamond, visible under magnification as a whitish or cloudy region where the crystal lattice has been disturbed. The term comes from the Afrikaans for 'seam' or 'knot' and is used principally in the South African diamond trade and onward through the wider international diamond market. Naats are clarity features rather than mineral inclusions, formed during the original crystal growth or by deformation in the mantle.
What a naat is
Diamonds grow as cubic crystals but can twin during growth or be deformed under mantle stress. At a twinning plane or grain boundary, the lattice orientation changes abruptly. Where the change is sharp enough to alter the local refractive index, light passing through the boundary is scattered rather than transmitted cleanly. The result is a visible streak, line, or patch that looks whitish, cloudy, or hazy under magnification, even though there is no foreign material at the location.
Effect on grade and value
Naats are clarity features and are recorded on plotting diagrams in the same way as crystals, feathers, and other internal features. Their effect on grade depends on size, position, and visibility: a small naat near the girdle that is invisible at 10x face-up may have minimal grade impact, while a prominent naat in the table area can pull a stone several grades below the equivalent stone without one. In severe cases the naat reduces brilliance and transparency face-up, causing a noticeable cloudy patch that affects appearance well beyond the strict grade.
Cutters work to position naats below the girdle or in the pavilion where possible, and to orient the rough so that the twinning plane lies along a less visible axis. A well-cut stone may have a significant naat that is well-managed; a poorly cut stone may have a small naat that nonetheless dominates appearance.
Identification
Naats are identified under standard 10x loupe or microscope examination by their characteristic appearance — soft-edged whitish lines or patches that follow lattice planes — and by the absence of any inclusion crystal at the location. Cross-polarised light shows the strain pattern around the boundary and confirms the twinning interpretation. Experienced graders distinguish naats from clouds, graining, and other lattice features as a matter of routine.