3926 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
pits are evident across habit types (see Figure 6b). Similar
features have been identified on larger diamonds subjected
to alluvial damage (e.g., Harris et al., 2022), where attri-
tion pits called “chatter marks” (Figure 6c) can be linked
to saltation-type sediment flow (particles bouncing along
riverbeds), and abrasion lines (Figure 6d) to faster mov-
ing environments where the particles (usually bigger dia-
monds) are dragged or rolled along the ground. Similar
flow-dynamics exist in the comminution circuit (Figure 1),
where scrubbing introduces a ‘tumbling’ action (shear force
‘attrition’) to an ore-water mix, breaking up rock agglom-
erates and potentially also diamond aggregates. Moreover,
vibrational screening, can lead to abrasion damage primar-
ily on larger diamonds, as particles failing to pass through
a size-constrained mesh are dragged across the screen to the
oversize stream. Another potential high-risk area for parti-
cle attrition damage arises during the pneumatic conveying
of free diamonds from Fines Dense Medium Separation to
recovery (Figure 1).
The concave fracture patterns observed at the corners
(vertices) of octahedral and macel crystals are often accom-
panied by visible impact distortion of the crystal lattice
(e.g., Figure 6e, f), where the affected vertex appears flat-
tened, and a concave deformation zone extends from the
surface downward into the diamond, causing internal frac-
turing and a noticeable darkening in colour. Additionally,
these stones frequently display recurring internal rainbow
colours known as Newton’s Rings when viewed under an
Figure 6. Mechanically induced diamond breakage patterns. (a) irregular wedge-shaped attrition marks on the surface of a
dodecahedral diamond. (b) a CT image of ‘tram-line’ abrasion pits on the surface of multiple diamond morphologies. (c) an
alluvial diamond (~3 mm) from Namibia exhibiting chatter marks from alluvial damage, taken from Harris et al. (2022). (d)
a 2 -3 mm alluvial diamond from Namaqualand (South Africa) exhibiting heavy frosting and abrasion pits, taken from Harris
et al. (2022). (e) rainbow colours emanating from within a distorted octahedral diamond aggregate. (f) a triangular shaped
macel diamond exhibiting conchoidal fracture on the corner and internal distortion revealed by the presence of Newton’s rings
pits are evident across habit types (see Figure 6b). Similar
features have been identified on larger diamonds subjected
to alluvial damage (e.g., Harris et al., 2022), where attri-
tion pits called “chatter marks” (Figure 6c) can be linked
to saltation-type sediment flow (particles bouncing along
riverbeds), and abrasion lines (Figure 6d) to faster mov-
ing environments where the particles (usually bigger dia-
monds) are dragged or rolled along the ground. Similar
flow-dynamics exist in the comminution circuit (Figure 1),
where scrubbing introduces a ‘tumbling’ action (shear force
‘attrition’) to an ore-water mix, breaking up rock agglom-
erates and potentially also diamond aggregates. Moreover,
vibrational screening, can lead to abrasion damage primar-
ily on larger diamonds, as particles failing to pass through
a size-constrained mesh are dragged across the screen to the
oversize stream. Another potential high-risk area for parti-
cle attrition damage arises during the pneumatic conveying
of free diamonds from Fines Dense Medium Separation to
recovery (Figure 1).
The concave fracture patterns observed at the corners
(vertices) of octahedral and macel crystals are often accom-
panied by visible impact distortion of the crystal lattice
(e.g., Figure 6e, f), where the affected vertex appears flat-
tened, and a concave deformation zone extends from the
surface downward into the diamond, causing internal frac-
turing and a noticeable darkening in colour. Additionally,
these stones frequently display recurring internal rainbow
colours known as Newton’s Rings when viewed under an
Figure 6. Mechanically induced diamond breakage patterns. (a) irregular wedge-shaped attrition marks on the surface of a
dodecahedral diamond. (b) a CT image of ‘tram-line’ abrasion pits on the surface of multiple diamond morphologies. (c) an
alluvial diamond (~3 mm) from Namibia exhibiting chatter marks from alluvial damage, taken from Harris et al. (2022). (d)
a 2 -3 mm alluvial diamond from Namaqualand (South Africa) exhibiting heavy frosting and abrasion pits, taken from Harris
et al. (2022). (e) rainbow colours emanating from within a distorted octahedral diamond aggregate. (f) a triangular shaped
macel diamond exhibiting conchoidal fracture on the corner and internal distortion revealed by the presence of Newton’s rings