GIA Knowledge Sessions Webinar - recorded live on September 3, 2020.
Naturally colored green diamonds are among the rarest of all colored diamonds. Unlike other diamonds that get their color deep in the earth, most green diamonds come into contact with radioactive fluids near the earth’s surface that create structural defects and produce their green color. Diamonds can also be turned green by irradiation treatment. Can natural green diamonds be separated from their treated counterparts? Unravel their mysteries with Senior Research Scientist Dr. Mike Breeding.
Read more of Dr. Mike Breeding's research:
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Questions answered by Dr. Karen Smit during the live webinar:
Q. What about if you do the opposite with a brownish-green diamond -- leave it at an extremely cold temperature for a long period of time?
A. As far as I’m aware, there is no effect of cold temperature on the color. Diamonds are routinely cooled to liquid nitrogen temperatures (77K) for visible and photoluminescence spectroscopy, and there is no color change observed during these analyses.
Q. What is the chemical composition of green and brown trains/spots? It appears to be outside of the crystal structure of diamond? Is it Fe-related material? Since the green spot changed into brown color as temperature increased?
A. Yes, the defect composition does change during heating. For green stains, the defect is the neutral vacancy (GR1). During heating, these vacancies combine with nitrogen in the diamond lattice to form new defects with darker coloration.
Q. Would it be possible to cut and polish a diamond keeping the green surface inclusions so that as a finished stone it would have these patterns? It would make a wonder stone for a piece of jewelry
A. Yes, it is indeed possible to preserve the green and brown radiation stains during cutting and polishing. Many “finished” diamonds still have stains visible under magnification.
Q. Do you think it’s possible to synthesize green diamonds in a lab?
A. Yes, it is possible to produce green coloration in the lab.
Q. Is it true that black HPHT is actually treated green most of the time?
A. It is certainly true that the saturation of any color can give a diamond a darker overall appearance. Dark colors can also be due to the presence of abundant dark metallic inclusions.
Q. Why are H3 defects termed H3 and not for example 2NV which would be more descriptive?
A. My understanding is that “H3” “N3” etc. are historical terminology that was in place prior to the defect being identified.
Q. Are Green diamond expensive than other colours?
A. Diamond price is dependent on many factors that include color, clarity, size and the cut of the stone. Natural green diamonds are certainly among the rarest diamonds, though there are also rare red diamonds, rare blue diamonds, and rare large colorless diamonds that can fetch high prices.
Q. If blue or green color is originated in defects in crystallite, is there a difference from ordinary colorless diamonds in mechanical properties which may be influent for hardness (cracking or crystal habits) or cutting difficulty?
A. Regardless of diamond color, the hardness of diamond remains the same. Polishing difficulty can be affected depending on the crystallographic plane that is being polished (cubic plane vs octahedral plane). Green diamonds have other polishing challenges, for example, if they are sufficiently heated during polishing, the color may be affected and they may turn brown.
Q. If alpha produces surface coloration, where does the natural deeper body green color come from?
A. Beta and Gamma radiation can penetrate deeper into the diamond. In nature, potassium-40 undergoes beta decay. Potassium is common in micas, feldspar and clay minerals.
Q. Two Questions - I missed the definition of two things:
1. H3
2. Vacancy
Can you please explain each quickly?
Thank you
A. H3 is 2 nitrogens around a vacancy. Vacancy is where the diamond lattice has a “missing” carbon atom.
