Temperature effects on radiation stains in natural diamonds

Effect of Nitrogen Impurities on the Raman Line Width in Diamond, Revisited

“…Thus, the study of Raman spectra with an emphasis on the line position and width can help in the characterization of diamonds and diamond-related materials. This message has been exploited in a prodigious number of works [11][12][13][14][15][16][17][18][19][20].…”

Iridescence in Metamorphic "Rainbow" Hematite

“…Depending on the amount of vacancies and the other impurities and defects present, green diamonds colored by GR1 typically have pure green or blue-green hues (figure 3); irradiation of a light yellow diamond produces a greener color, while irradiation of a colorless diamond causes a bluer color. Most naturally irradiated diamonds have shallow green "skins" or spots on the crystal surface that produce most of the green appearance (Vance and Milledge, 1972;Vance et al, 1973;Kane, 1979b;Fritsch and Shigley, 1991;Roskin, 2000;Eaton-Magaña and Moe, 2016). Upon faceting, these shallow areas of radiation damage are typically removed and the apparently green rough diamond shows little to no color as a finished cut stone (figure 5, bottom row).…”

“…The shallow nature (approximately 20 µm thick) of the green spots and zones indicates that the radiation damage is primarily caused by alpha particles (see box A for radiation types and sources), most likely from uranium decay (Vance et al, 1973;Nasdala et al, 2013). These spots have been experimen-tally shown to rapidly turn from green to brown at temperatures of 550-600°C (Nasdala et al, 2013;Eaton-Magaña and Moe, 2016), indicating that diamonds with green radiation damage must have resided at depths less than about 24 km (assuming average geothermal gradient of 25°C/km). Some green diamonds, however, show color zones that penetrate much deeper than 20 µm, sometimes even throughout the stones.…”

“…Radiation stains occur as either green or brown patches of color on the surface of a rough diamond or within fractures. The radiation damage initially has a forest green color (often very dark green, depending on the dosage of the exposure) and then turns olive green at temperatures between 500 and 600°C and a reddish brown to dark brown at higher temperatures (Vance et al, 1973;Nasdala et al, 2013;Eaton-Magaña and Moe, 2016). Some experiments have shown that the brown stains disappear at temperatures above 1400°C (Eaton-Magaña and Moe, 2016).…”

“…Damage to the atomic lattice by alpha particles causes a slight volume expansion in the diamond and an elevated surface at the locus of the stain (Nasdala et al, 2013). The green or brown color penetrates to depths of usually not much more than 20 µm (0.02 mm), creating a shallow zone of green color adjacent to the stain(s) (figure 9, A-B; Nasdala et al, 2013;Eaton-Magaña and Moe, 2016).…”