GIA Diamond Treatments and Synthetics 2 — Questions and Answers
Question 1: Which spectroscopic feature is most diagnostic for identifying a CVD-grown synthetic diamond?
- Strong absorption at 415 nm
- Si-V defect emission at 737 nm (Correct answer)
- Cape series lines at 478 nm
- H3 center at 503 nm
Correct answer: Si-V defect emission at 737 nm
CVD synthetics commonly show a silicon-vacancy (Si-V) defect center emitting at 737 nm due to silicon contamination from the reactor walls.
Question 2: A diamond shows graining that appears whitish and reflects light differently than the surrounding crystal. This most likely indicates:
- Laser drilling
- Fracture filling
- High-pressure high-temperature (HPHT) treatment (Correct answer)
- Irradiation followed by annealing
Correct answer: High-pressure high-temperature (HPHT) treatment
HPHT treatment can produce or alter graining patterns, sometimes creating whitish graining visible under magnification as the crystal structure is stressed.
Question 3: What is the primary purpose of annealing a diamond after irradiation?
- To remove all color induced by irradiation
- To convert green surface color to a stable body color (Correct answer)
- To eliminate radioactivity
- To improve clarity grade
Correct answer: To convert green surface color to a stable body color
Annealing after irradiation converts the unstable green skin color into deeper, more stable colors such as yellow, orange, or brown throughout the stone.
Question 4: Which characteristic is shared by both HPHT-treated and natural Type IIa diamonds?
- Presence of nitrogen aggregates in B form
- Absence or very low nitrogen content (Correct answer)
- Strong Cape absorption series
- Brown graining patterns
Correct answer: Absence or very low nitrogen content
Both natural Type IIa diamonds and HPHT-treated diamonds that have been decolorized exhibit very low or negligible nitrogen, which is why treatment is effective on Type IIa candidates.
Question 5: The 'flash effect' seen in fracture-filled diamonds under magnification appears as:
- A red or orange hue throughout the stone
- Alternating blue-purple and orange-yellow colors along the fracture (Correct answer)
- A white haze at the fracture plane
- Green fluorescence along the filled area
Correct answer: Alternating blue-purple and orange-yellow colors along the fracture
The flash effect — alternating blue-purple and orange-yellow iridescence — is caused by thin-film interference of the glass-like filler within the fracture.
Question 6: A fancy vivid blue diamond is submitted for GIA grading. Which test would best differentiate a natural-color blue from an irradiated blue?
- Microscopic examination of inclusions
- Spectroscopic analysis of the absorption pattern (Correct answer)
- Measurement of specific gravity
- UV fluorescence color comparison
Correct answer: Spectroscopic analysis of the absorption pattern
Spectroscopic analysis reveals distinct absorption features — naturally blue (Type IIb) diamonds show a different boron-related absorption pattern compared to the broad H3/GR1 bands in irradiated blue diamonds.
Question 7: Which of the following statements about lab-grown diamonds is accurate regarding their hardness?
- Lab-grown diamonds are softer than natural diamonds due to faster growth
- Lab-grown diamonds have the same hardness (10 on Mohs scale) as natural diamonds (Correct answer)
- Lab-grown diamonds rate 9.5 on the Mohs scale
- Hardness varies by growth method (CVD vs. HPHT)
Correct answer: Lab-grown diamonds have the same hardness (10 on Mohs scale) as natural diamonds
Lab-grown diamonds are chemically and physically identical to natural diamonds, including having the same hardness of 10 on the Mohs scale regardless of growth method.
GIA Diamond Treatments and Synthetics 2
Which spectroscopic feature is most diagnostic for identifying a CVD-grown synthetic diamond?