CGA Colored Gemstones & Pearl Evaluation Flashcards

Which color is considered the most valuable for a ruby?

Answer: Vivid red ('pigeon's blood')

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.

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

Answer: Color zoning and natural inclusions

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.

What is 'pleochroism' in colored gemstones?

Answer: The ability to display different colors when viewed from different angles

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.

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

Answer: Ruby, emerald, and sapphire

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.

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

Answer: 'Jardin' (garden) of three-phase inclusions

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).

For a CGA appraisal, what does 'treatment disclosure' mean for colored gemstones?

Answer: Informing the client of any enhancements that alter the gem's appearance or durability

Treatment disclosure requires appraisers to identify and disclose any enhancements (e.g., heat treatment, fracture filling, irradiation) that have altered the gemstone's natural appearance, color, or durability.