CGA CGA Colored Gemstones & Pearl Evaluation 2

Question 1

What is the primary factor that distinguishes a natural pearl from a cultured pearl?

Accepted Answer

Whether a human-inserted nucleus was used to stimulate nacre production

Answer

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?

Accepted Answer

The iridescent calcium carbonate layers that form a pearl

Answer

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?

Accepted Answer

South Sea pearls

Answer

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?

Accepted Answer

The iridescent play of color across the surface of a pearl

Answer

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?

Accepted Answer

X-ray or endoscope

Answer

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.

(CGA) Certified Gemologist Appraiser Practice Test

(CGA) Certified Gemologist Appraiser Practice Test

CGA CGA Colored Gemstones & Pearl Evaluation 2