CGA Gem Identification & Grading Techniques 5

Question 1

What distinguishes a 'Type IIa' diamond from a 'Type Ia' diamond in terms of chemical composition?

Accepted Answer

Type IIa contains virtually no nitrogen; Type Ia contains nitrogen aggregates

Answer

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?

Accepted Answer

A calcium lithium aluminum tourmaline often showing triangular color zoning

Answer

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?

Accepted Answer

It raises the grade because even distribution is generally desirable

Answer

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?

Accepted Answer

Color change from green in daylight to red in incandescent light

Answer

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?

Accepted Answer

GIA GemSet / ColorMaster system

Answer

GIA developed the GemSet and ColorMaster tools to provide standardized color communication using hue, tone, and saturation references for colored stone grading.

(CGA) Certified Gemologist Appraiser Practice Test

(CGA) Certified Gemologist Appraiser Practice Test

CGA Gem Identification & Grading Techniques 5