Diamond resorption in non-igneous settings evidenced by AFM of fine surface textures coincident with radiation stains.

Roy Bassoo, Taryn Linzmeyer, Mike Breeding, Bernd Zechmann, Sally Eaton-Magaña,
Diamond resorption in non-igneous settings evidenced by AFM of fine surface textures coincident with radiation stains, Lithos, Volumes 518–519, 2025, 108315, ISSN 0024-4937, DOI: https://doi.org/10.1016/j.lithos.2025.108315.
<br>
<br>
(https://www.sciencedirect.com/science/article/pii/S0024493725003743)
<br>
<br>
Abstract: Rarely documented fine negative surface topography coincident with “radiation stains” on 16 diamonds are investigated by atomic force microscopy (AFM) to assess surface feature morphology and infer formation conditions. These features are inferred to derive from post-irradiation resorption by oxidizing pore fluids at relatively low temperatures when residing in sedimentary rocks. We document the presence of circular, rounded, acicular, bladed, cubic, prismatic, and tabular surface features exclusively coincident with radiation stains. Surface areas are ≤300 μm2 and 17 ± 43 μm2 on average. Acicular features have the highest mean length-width ratio of 8 ± 4. Bladed, prismatic, and circular to rounded features have mean length-width ratios of 3 ± 1, 2 ± 2, and ∼ 1 respectively. These features penetrate into the diamond with depths of 4 to <240 nm and most have solely flat-bottomed morphologies. Circular features have the highest mean depths of 115 ± 71 nm. Bladed, acicular, prismatic, cubic, rounded features have mean depths of 54 ± 36 nm, 32 ± 21 nm, 33 ± 22 nm, 23 ± 5 nm, and 22 ± 15 nm respectively. Raman transects across radiation stains hosting these features have higher 1332 cm−1 full width at half maximum (FWHM) values than in colorless zones on the same diamond indicating the presence of tetragonal to tetrahedral amorphous carbon. During residence in ancient conglomerates, diamonds could be subjected to irradiation by nearby radioactive minerals which transforms irradiated sites to amorphous carbon. We suggest when amorphous carbon is exposed to oxidizing pore fluids it preferentially dissolves and leaves behind a resorption pit coincident with radiation stains. Our study suggests diamonds can be resorbed in non-igneous settings and likely during residence in ancient sedimentary rocks.
<br>
Keywords: Diamonds; Green diamonds; Radiation stains; Morphology; Conglomerates; Resorption