CGA Gem Identification & Grading Techniques 5 — Questions and Answers
Question 1: What distinguishes a 'Type IIa' diamond from a 'Type Ia' diamond in terms of chemical composition?
- Type IIa contains boron; Type Ia contains no impurities
- Type IIa contains virtually no nitrogen; Type Ia contains nitrogen aggregates (Correct answer)
- Type IIa is always colored; Type Ia is always colorless
- Type IIa has lower hardness than Type Ia
Correct answer: Type IIa contains virtually no nitrogen; Type Ia contains nitrogen aggregates
Type IIa diamonds contain virtually no nitrogen impurities, making them often colorless and chemically pure, while Type Ia contains nitrogen in aggregated form.
Question 2: Which of the following best describes the 'liddicoatite' variety of tourmaline, often seen in gem identification scenarios?
- A calcium lithium aluminum tourmaline often showing triangular color zoning (Correct answer)
- An iron-rich tourmaline always colored black
- A chrome-bearing tourmaline from Brazil
- A colorless tourmaline used as a diamond simulant
Correct answer: A calcium lithium aluminum tourmaline often showing triangular color zoning
Liddicoatite is a calcium lithium aluminum tourmaline species frequently displaying complex triangular color zoning patterns in cross-section.
Question 3: A gemologist is grading a fancy colored diamond and notes an even distribution of color throughout the stone. How does uniform color distribution affect the grade?
- It lowers the grade because concentrated color is preferred
- It raises the grade because even distribution is generally desirable (Correct answer)
- Color distribution is not considered in fancy color grading
- It only matters for yellow and brown diamonds
Correct answer: It raises the grade because even distribution is generally desirable
In GIA fancy color grading, even color distribution is viewed positively and contributes to a higher overall color grade for fancy colored diamonds.
Question 4: What optical characteristic distinguishes alexandrite from other chrysoberyl varieties?
- Extreme hardness of 9.5 on the Mohs scale
- Color change from green in daylight to red in incandescent light (Correct answer)
- Star effect caused by rutile needles
- Very high dispersion causing strong fire
Correct answer: Color change from green in daylight to red in incandescent light
Alexandrite displays a dramatic color change from green or bluish-green in daylight to red or purplish-red in incandescent light due to chromium's absorption properties.
Question 5: During appraisal documentation of a colored gemstone, which GIA system is used to communicate color using standardized hue, tone, and saturation descriptions?
- Munsell Color System
- GemDialogue
- GIA GemSet / ColorMaster system (Correct answer)
- Pantone Gemstone Reference
Correct answer: GIA GemSet / ColorMaster system
GIA developed the GemSet and ColorMaster tools to provide standardized color communication using hue, tone, and saturation references for colored stone grading.
Question 6: Which fluorescence characteristic under shortwave UV can help distinguish natural blue sapphires from blue synthetic sapphires made by the Verneuil (flame fusion) process?
- Natural sapphires fluoresce strong red; Verneuil synthetics show no fluorescence
- Natural sapphires show no reaction; Verneuil synthetics often fluoresce chalky blue-white (Correct answer)
- Both fluoresce identically under shortwave UV
- Natural sapphires fluoresce yellow; synthetics fluoresce green
Correct answer: Natural sapphires show no reaction; Verneuil synthetics often fluoresce chalky blue-white
Verneuil synthetic sapphires often exhibit a strong chalky blue-white fluorescence under shortwave UV, while most natural sapphires show little or no reaction.
Question 7: A CGA appraiser notes that an emerald has a clarity grade described as 'eye-clean.' What does this mean in practical terms?
- The stone has no inclusions whatsoever under any magnification
- No inclusions are visible to the unaided eye at a normal viewing distance (Correct answer)
- The stone has been clarity-enhanced to remove all surface inclusions
- The clarity grade applies only to the table facet
Correct answer: No inclusions are visible to the unaided eye at a normal viewing distance
An 'eye-clean' stone has no inclusions visible to the naked eye at typical viewing distance, though inclusions may still be present under magnification.
CGA Gem Identification & Grading Techniques 5
What distinguishes a 'Type IIa' diamond from a 'Type Ia' diamond in terms of chemical composition?