GIA COLORED STONE ESSENTIALS TESTS – 70
QUESTIONS With Correct Answers & Detailed
Rationales.
1. The term phenomenon in gemology refers to:
A. The chemical composition
B. Light-related optical effects
C. A gem’s durability
D. The geographic origin
Answer: B
Rationale: Phenomena are unusual optical effects such as asterism,
chatoyancy, color change, etc., caused by interactions between light and
internal structures.
2. Which gem most commonly shows pleochroism?
A. Emerald
B. Peridot
C. Tanzanite
D. Garnet
Answer: C
Rationale: Tanzanite (zoisite) is strongly pleochroic, typically showing blue–
purple–brown depending on viewing direction.
3. The most important factor affecting peridot value:
A. RI
B. Origin
,C. Color
D. Transparency
Answer: C
Rationale: The ideal peridot color is pure, vibrant, medium-tone green
without brownish or yellowish modifiers.
4. Color-change in alexandrite is caused by:
A. Chromium
B. Iron
C. Cobalt
D. Titanium
Answer: A
Rationale: Chromium causes the unique absorption that makes alexandrite
appear green in daylight and red under incandescent light.
5. The phenomenon seen in star sapphire:
A. Chatoyancy
B. Labradorescence
C. Asterism
D. Opalescence
Answer: C
Rationale: Asterism is a star-like pattern caused by oriented rutile silk
inclusions.
6. Refractive index is measured with:
A. Spectroscope
B. Dichroscope
, C. Polariscope
D. Refractometer
Answer: D
Rationale: RI is the ratio of the speed of light in air vs. the gem; measured
using a refractometer and RI liquid.
7. A gem with double refraction will show:
A. No birefringence
B. Single reading
C. Two different RI values
D. Only bodycolor
Answer: C
Rationale: Doubly refractive stones split light into two rays, creating two
refractive index readings.
8. The best indicator for separating ruby from red spinel:
A. Luster
B. RI & birefringence
C. Color
D. Hardness
Answer: B
Rationale: Ruby is doubly refractive with birefringence; spinel is singly
refractive.
9. A gem treatment that adds color or clarity by introducing foreign
material:
A. Heat
B. Diffusion
QUESTIONS With Correct Answers & Detailed
Rationales.
1. The term phenomenon in gemology refers to:
A. The chemical composition
B. Light-related optical effects
C. A gem’s durability
D. The geographic origin
Answer: B
Rationale: Phenomena are unusual optical effects such as asterism,
chatoyancy, color change, etc., caused by interactions between light and
internal structures.
2. Which gem most commonly shows pleochroism?
A. Emerald
B. Peridot
C. Tanzanite
D. Garnet
Answer: C
Rationale: Tanzanite (zoisite) is strongly pleochroic, typically showing blue–
purple–brown depending on viewing direction.
3. The most important factor affecting peridot value:
A. RI
B. Origin
,C. Color
D. Transparency
Answer: C
Rationale: The ideal peridot color is pure, vibrant, medium-tone green
without brownish or yellowish modifiers.
4. Color-change in alexandrite is caused by:
A. Chromium
B. Iron
C. Cobalt
D. Titanium
Answer: A
Rationale: Chromium causes the unique absorption that makes alexandrite
appear green in daylight and red under incandescent light.
5. The phenomenon seen in star sapphire:
A. Chatoyancy
B. Labradorescence
C. Asterism
D. Opalescence
Answer: C
Rationale: Asterism is a star-like pattern caused by oriented rutile silk
inclusions.
6. Refractive index is measured with:
A. Spectroscope
B. Dichroscope
, C. Polariscope
D. Refractometer
Answer: D
Rationale: RI is the ratio of the speed of light in air vs. the gem; measured
using a refractometer and RI liquid.
7. A gem with double refraction will show:
A. No birefringence
B. Single reading
C. Two different RI values
D. Only bodycolor
Answer: C
Rationale: Doubly refractive stones split light into two rays, creating two
refractive index readings.
8. The best indicator for separating ruby from red spinel:
A. Luster
B. RI & birefringence
C. Color
D. Hardness
Answer: B
Rationale: Ruby is doubly refractive with birefringence; spinel is singly
refractive.
9. A gem treatment that adds color or clarity by introducing foreign
material:
A. Heat
B. Diffusion
