Gemology Certification Gemology Gem Identification Techniques 2 — Questions and Answers
Question 1: Which optical phenomenon causes a star-shaped reflection in cabochon-cut gems like star sapphire?
- Asterism (Correct answer)
- Chatoyancy
- Adularescence
- Labradorescence
Correct answer: Asterism
Asterism is caused by intersecting needle-like inclusions (usually rutile) that reflect light into a star pattern.
Question 2: A gemologist uses a dichroscope and observes two different colors in a stone. This indicates the stone is:
- Isotropic
- Pleochroic (Correct answer)
- Fluorescent
- Phosphorescent
Correct answer: Pleochroic
Pleochroism is the property of showing different colors when viewed from different crystallographic directions.
Question 3: The Chelsea colour filter was originally developed to distinguish which two stones?
- Ruby and garnet
- Emerald and green glass (Correct answer)
- Sapphire and aquamarine
- Jade and serpentine
Correct answer: Emerald and green glass
The Chelsea filter was designed to separate natural emeralds (appear red) from green glass and paste imitations (appear green).
Question 4: When a gem shows a specific gravity of 4.00, which of these stones is most likely the candidate?
- Quartz (2.66)
- Topaz (3.53)
- Corundum (4.00) (Correct answer)
- Diamond (3.52)
Correct answer: Corundum (4.00)
Corundum (ruby and sapphire) has a specific gravity of approximately 4.00, making it the correct match.
Question 5: Which inclusion type in a diamond is most useful for confirming natural versus synthetic origin?
- Feathers
- Metallic flux inclusions (Correct answer)
- Clouds
- Needles
Correct answer: Metallic flux inclusions
Metallic flux inclusions are characteristic of flux-grown synthetic diamonds and do not occur in natural diamonds.
Question 6: Measuring the birefringence of a stone involves comparing:
- Hardness on two axes
- The two refractive indices of an anisotropic gem (Correct answer)
- Specific gravity in two liquids
- Fluorescence under UV and visible light
Correct answer: The two refractive indices of an anisotropic gem
Birefringence is the numerical difference between the highest and lowest refractive indices of a doubly refractive gem.
Question 7: A stone immersed in methylene iodide (specific gravity ~3.32) floats to the surface. What can you conclude?
- Its SG is greater than 3.32
- Its SG is less than 3.32 (Correct answer)
- Its SG equals 3.32
- The stone is synthetic
Correct answer: Its SG is less than 3.32
A stone floats in a heavy liquid when its specific gravity is lower than that of the liquid.
Gemology Certification Gemology Gem Identification Techniques 2
Which optical phenomenon causes a star-shaped reflection in cabochon-cut gems like star sapphire?