CGA CGA Colored Gemstones & Pearl Evaluation

Question 1

Which color is considered the most valuable for a ruby?

Accepted Answer

Vivid red ('pigeon's blood')

Answer

The most prized ruby color is 'pigeon's blood' — a vivid, pure red with a slight blue fluorescence, historically associated with rubies from the Mogok Valley in Myanmar.

Question 2

A gemologist wants to distinguish a natural sapphire from a synthetic sapphire. Which characteristic would be most useful?

Accepted Answer

Color zoning and natural inclusions

Answer

Natural sapphires typically show curved or angular color zoning, silk (rutile needles), and other natural inclusions that are absent or different in synthetic sapphires grown in a lab.

Question 3

What is 'pleochroism' in colored gemstones?

Accepted Answer

The ability to display different colors when viewed from different angles

Answer

Pleochroism is the optical phenomenon in which a gemstone displays different colors or shades when viewed from different crystallographic directions due to selective absorption of light.

Question 4

The 'big three' colored gemstones in the jewelry industry are:

Accepted Answer

Ruby, emerald, and sapphire

Answer

Ruby, emerald, and sapphire are referred to as the 'big three' colored gemstones due to their historical prestige, consumer demand, and typically high market values.

Question 5

What type of inclusion is most characteristic of natural Colombian emeralds?

Accepted Answer

'Jardin' (garden) of three-phase inclusions

Answer

Colombian emeralds typically contain three-phase inclusions consisting of a solid crystal, liquid, and gas bubble within the same cavity, collectively called 'jardin' (French for garden).

(CGA) Certified Gemologist Appraiser Practice Test

(CGA) Certified Gemologist Appraiser Practice Test

CGA CGA Colored Gemstones & Pearl Evaluation