CGA CGA Colored Gemstones & Pearl Evaluation 2 — Questions and Answers
Question 1: What is the primary factor that distinguishes a natural pearl from a cultured pearl?
- Size
- Luster
- Whether a human-inserted nucleus was used to stimulate nacre production (Correct answer)
- Whether the pearl came from saltwater or freshwater
Correct answer: Whether a human-inserted nucleus was used to stimulate nacre production
Natural pearls form entirely without human intervention, while cultured pearls are produced by inserting a bead nucleus or tissue graft into a mollusk to stimulate nacre deposition around it.
Question 2: What is 'nacre' in pearl grading?
- The outer protective layer of the mollusk shell
- The iridescent calcium carbonate layers that form a pearl (Correct answer)
- The color of the pearl's body tone
- The thread used to string pearls in a necklace
Correct answer: The iridescent calcium carbonate layers that form a pearl
Nacre is the iridescent material composed of layers of aragonite crystals and conchiolin that mollusks secrete around an irritant or nucleus, forming the pearl.
Question 3: Which type of pearl is most valuable and commands the highest prices in the US market?
- Freshwater pearls
- Akoya pearls
- South Sea pearls (Correct answer)
- Tahitian pearls
Correct answer: South Sea pearls
South Sea pearls, produced by Pinctada maxima oysters in Australia, Indonesia, and the Philippines, are the largest and most valuable cultured pearls due to their size (10–20mm), thick nacre, and satiny luster.
Question 4: What does 'orient' mean when evaluating pearl quality?
- The geographic origin of the pearl
- The iridescent play of color across the surface of a pearl (Correct answer)
- The orientation of the pearl's drill hole
- The roundness of the pearl
Correct answer: The iridescent play of color across the surface of a pearl
Orient refers to the iridescent shimmer of colors (pink, green, blue) that plays across the surface of high-quality pearls, caused by light interference within the layers of nacre.
Question 5: A CGA appraiser is valuing a strand of natural pearls. What instrument can help distinguish natural from cultured pearls?
- Refractometer
- X-ray or endoscope (Correct answer)
- Chelsea filter
- Polariscope
Correct answer: X-ray or endoscope
X-ray examination reveals the internal structure of a pearl; natural pearls show concentric growth rings throughout, while cultured pearls typically show a large nucleus with a thin nacre coating.
Question 6: What is the main characteristic that makes alexandrite valuable and distinctive?
- Its intense blue color rivaling sapphire
- Its dramatic color change from green in daylight to red in incandescent light (Correct answer)
- Its extreme hardness exceeding diamond
- Its high dispersion producing rainbow fire
Correct answer: Its dramatic color change from green in daylight to red in incandescent light
Alexandrite is prized for its dramatic color change phenomenon — appearing green to bluish-green in daylight and red to purplish-red under incandescent light — due to the selective absorption of light by chromium.
CGA CGA Colored Gemstones & Pearl Evaluation 2
What is the primary factor that distinguishes a natural pearl from a cultured pearl?